From: Stephen Hemminger <stephen@networkplumber.org> Date: 2021-07-14 15:13:27
Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
--> https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun 1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28 EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4 metric 100
So the host would pick the first or the second nexthop depending on ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss, time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the MTU is
lowered on the client side for this target. Through the GW-2 PMTUD does not,
all responses to ping are ICMP frag needed, which are not obeyed by the kernel.
In all failure cases mtu is not cashed on "ip route get".
--
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Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
--> https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun 1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28 EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4 metric 100
So the host would pick the first or the second nexthop depending on ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss, time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the MTU is
lowered on the client side for this target. Through the GW-2 PMTUD does not,
all responses to ping are ICMP frag needed, which are not obeyed by the kernel.
In all failure cases mtu is not cashed on "ip route get".
Looks like I'm in context of PMTU and also I'm working on implementing several
new test cases for pmtu.sh test, so I will take care of this one too
On Wed, Jul 14, 2021 at 05:11:45PM +0100, Vadim Fedorenko wrote:
On 14.07.2021 16:13, Stephen Hemminger wrote:
quoted
Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
--> https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun 1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28 EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4 metric 100
So the host would pick the first or the second nexthop depending on ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss, time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the MTU is
lowered on the client side for this target. Through the GW-2 PMTUD does not,
all responses to ping are ICMP frag needed, which are not obeyed by the kernel.
In all failure cases mtu is not cashed on "ip route get".
Looks like I'm in context of PMTU and also I'm working on implementing several
new test cases for pmtu.sh test, so I will take care of this one too
On Wed, Jul 14, 2021 at 05:11:45PM +0100, Vadim Fedorenko wrote:
quoted
On 14.07.2021 16:13, Stephen Hemminger wrote:
quoted
Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
--> https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun 1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28 EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4 metric 100
So the host would pick the first or the second nexthop depending on ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss, time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the MTU is
lowered on the client side for this target. Through the GW-2 PMTUD does not,
all responses to ping are ICMP frag needed, which are not obeyed by the kernel.
In all failure cases mtu is not cashed on "ip route get".
Looks like I'm in context of PMTU and also I'm working on implementing several
new test cases for pmtu.sh test, so I will take care of this one too
From: David Ahern <hidden> Date: 2021-07-14 18:12:29
On 7/14/21 11:51 AM, Vadim Fedorenko wrote:
On 14.07.2021 17:30, Ido Schimmel wrote:
quoted
On Wed, Jul 14, 2021 at 05:11:45PM +0100, Vadim Fedorenko wrote:
quoted
On 14.07.2021 16:13, Stephen Hemminger wrote:
quoted
Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
-->
https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU
greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline
kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun
1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28
EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4
metric 100
So the host would pick the first or the second nexthop depending on
ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works
through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss,
time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this
example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on
ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time
2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms
pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated
for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same
interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other
route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the
MTU is
lowered on the client side for this target. Through the GW-2 PMTUD
does not,
all responses to ping are ICMP frag needed, which are not obeyed by
the kernel.
In all failure cases mtu is not cashed on "ip route get".
Looks like I'm in context of PMTU and also I'm working on
implementing several
new test cases for pmtu.sh test, so I will take care of this one too
I believe that one is fixed by 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
The root cause of this problem is icmp's taking a path that the original
packet did not. i.e., the ICMP is received on device 1 and the exception
is created on that device but Rx chooses device 2 (a different leg in
the ECMP).
On Wed, Jul 14, 2021 at 11:42 PM David Ahern [off-list ref] wrote:
quoted
On 7/14/21 11:51 AM, Vadim Fedorenko wrote:
quoted
On 14.07.2021 17:30, Ido Schimmel wrote:
quoted
On Wed, Jul 14, 2021 at 05:11:45PM +0100, Vadim Fedorenko wrote:
quoted
On 14.07.2021 16:13, Stephen Hemminger wrote:
quoted
Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
-->
https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU
greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline
kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun
1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28
EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4
metric 100
So the host would pick the first or the second nexthop depending on
ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works
through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss,
time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this
example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on
ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time
2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms
pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated
for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same
interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other
route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the
MTU is
lowered on the client side for this target. Through the GW-2 PMTUD
does not,
all responses to ping are ICMP frag needed, which are not obeyed by
the kernel.
In all failure cases mtu is not cashed on "ip route get".
Looks like I'm in context of PMTU and also I'm working on
implementing several
new test cases for pmtu.sh test, so I will take care of this one too
I believe that one is fixed by 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
The root cause of this problem is icmp's taking a path that the original
packet did not. i.e., the ICMP is received on device 1 and the exception
is created on that device but Rx chooses device 2 (a different leg in
the ECMP).
Actual test was carried out in 5.13.0-rc5 kernel and also tested
5.14-rc1 kernel as well. This Issue is still reproduced.
From: Sam Kappen <hidden> Date: 2021-07-20 02:36:20
On Wed, Jul 14, 2021 at 11:42 PM David Ahern [off-list ref] wrote:
On 7/14/21 11:51 AM, Vadim Fedorenko wrote:
quoted
On 14.07.2021 17:30, Ido Schimmel wrote:
quoted
On Wed, Jul 14, 2021 at 05:11:45PM +0100, Vadim Fedorenko wrote:
quoted
On 14.07.2021 16:13, Stephen Hemminger wrote:
quoted
Begin forwarded message:
Date: Wed, 14 Jul 2021 13:43:51 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: stephen@networkplumber.org
Subject: [Bug 213729] New: PMTUD failure with ECMP.
https://bugzilla.kernel.org/show_bug.cgi?id=213729
Bug ID: 213729
Summary: PMTUD failure with ECMP.
Product: Networking
Version: 2.5
Kernel Version: 5.13.0-rc5
Hardware: x86-64
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: IPV4
Assignee: stephen@networkplumber.org
Reporter: skappen@mvista.com
Regression: No
Created attachment 297849
-->
https://bugzilla.kernel.org/attachment.cgi?id=297849&action=edit
Ecmp pmtud test setup
PMTUD failure with ECMP.
We have observed failures when PMTUD and ECMP work together.
Ping fails either through gateway1 or gateway2 when using MTU
greater than
1500.
The Issue has been tested and reproduced on CentOS 8 and mainline
kernels.
Kernel versions:
[root@localhost ~]# uname -a
Linux localhost.localdomain 4.18.0-305.3.1.el8.x86_64 #1 SMP Tue Jun
1 16:14:33
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost skappen]# uname -a
Linux localhost.localdomain 5.13.0-rc5 #2 SMP Thu Jun 10 05:06:28
EDT 2021
x86_64 x86_64 x86_64 GNU/Linux
Static routes with ECMP are configured like this:
[root@localhost skappen]#ip route
default proto static
nexthop via 192.168.0.11 dev enp0s3 weight 1
nexthop via 192.168.0.12 dev enp0s3 weight 1
192.168.0.0/24 dev enp0s3 proto kernel scope link src 192.168.0.4
metric 100
So the host would pick the first or the second nexthop depending on
ECMP's
hashing algorithm.
When pinging the destination with MTU greater than 1500 it works
through the
first gateway.
[root@localhost skappen]# ping -s1700 10.0.3.17
PING 10.0.3.17 (10.0.3.17) 1700(1728) bytes of data.
From 192.168.0.11 icmp_seq=1 Frag needed and DF set (mtu = 1500)
1708 bytes from 10.0.3.17: icmp_seq=2 ttl=63 time=0.880 ms
1708 bytes from 10.0.3.17: icmp_seq=3 ttl=63 time=1.26 ms
^C
--- 10.0.3.17 ping statistics ---
3 packets transmitted, 2 received, +1 errors, 33.3333% packet loss,
time 2003ms
rtt min/avg/max/mdev = 0.880/1.067/1.255/0.190 ms
The MTU also gets cached for this route as per rfc6754:
[root@localhost skappen]# ip route get 10.0.3.17
10.0.3.17 via 192.168.0.11 dev enp0s3 src 192.168.0.4 uid 0
cache expires 540sec mtu 1500
[root@localhost skappen]# tracepath -n 10.0.3.17
1?: [LOCALHOST] pmtu 1500
1: 192.168.0.11 1.475ms
1: 192.168.0.11 0.995ms
2: 192.168.0.11 1.075ms !H
Resume: pmtu 1500
However when the second nexthop is picked PMTUD breaks. In this
example I ping
a second interface configured on the same destination
from the same host, using the same routes and gateways. Based on
ECMP's hashing
algorithm this host would pick the second nexthop (.2):
[root@localhost skappen]# ping -s1700 10.0.3.18
PING 10.0.3.18 (10.0.3.18) 1700(1728) bytes of data.
From 192.168.0.12 icmp_seq=1 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=2 Frag needed and DF set (mtu = 1500)
From 192.168.0.12 icmp_seq=3 Frag needed and DF set (mtu = 1500)
^C
--- 10.0.3.18 ping statistics ---
3 packets transmitted, 0 received, +3 errors, 100% packet loss, time
2062ms
[root@localhost skappen]# ip route get 10.0.3.18
10.0.3.18 via 192.168.0.12 dev enp0s3 src 192.168.0.4 uid 0
cache
[root@localhost skappen]# tracepath -n 10.0.3.18
1?: [LOCALHOST] pmtu 9000
1: 192.168.0.12 3.147ms
1: 192.168.0.12 0.696ms
2: 192.168.0.12 0.648ms
pmtu 1500
2: 192.168.0.12 0.761ms !H
Resume: pmtu 1500
The ICMP frag needed reaches the host, but in this case it is ignored.
The MTU for this route does not get cached either.
It looks like mtu value from the next hop is not properly updated
for some
reason.
Test Case:
Create 2 networks: Internal, External
Create 4 virtual machines: Client, GW-1, GW-2, Destination
Client
configure 1 NIC to internal with MTU 9000
configure static route with ECMP to GW-1 and GW-2 internal address
GW-1, GW-2
configure 2 NICs
- to internal with MTU 9000
- to external MTU 1500
- enable ip_forward
- enable packet forward
Target
configure 1 NIC to external MTU with 1500
configure multiple IP address(say IP1, IP2, IP3, IP4) on the same
interface, so
ECMP's hashing algorithm would pick different routes
Test
ping from client to target with larger than 1500 bytes
ping the other addresses of the target so ECMP would use the other
route too
Results observed:
Through GW-1 PMTUD works, after the first frag needed message the
MTU is
lowered on the client side for this target. Through the GW-2 PMTUD
does not,
all responses to ping are ICMP frag needed, which are not obeyed by
the kernel.
In all failure cases mtu is not cashed on "ip route get".
Looks like I'm in context of PMTU and also I'm working on
implementing several
new test cases for pmtu.sh test, so I will take care of this one too
I believe that one is fixed by 2fbc6e89b2f1403189e624cabaf73e189c5e50c6
The root cause of this problem is icmp's taking a path that the original
packet did not. i.e., the ICMP is received on device 1 and the exception
is created on that device but Rx chooses device 2 (a different leg in
the ECMP).
Actual test was carried out in 5.13.0-rc5 kernel and also tested
5.14-rc1 kernel as well. This Issue is still reproduced.