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Downs't watch on MTU change #1601

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nevzorofff opened this issue Jan 6, 2018 · 5 comments
Closed

Downs't watch on MTU change #1601

nevzorofff opened this issue Jan 6, 2018 · 5 comments
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@rwestphal
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ospf question Not a bug

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@nevzorofff
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I use MPD daemon to make VPN links, an don inactive or non existend interfaces ospfd use MTU=1500 bytes. When links up MTU changes to different value, but ospfd uses 1500 and we get MTU mismatch on other side.
@rwestphal rwestphal self-assigned this Jan 11, 2018
@rwestphal
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Given the other issue you opened I assume you're using FreeBSD.

I can not reproduce this problem here using FreeBSD 11.1. zebra is able to detect MTU changes and notify the client daemons about them. Please take a look:

bash:

root@freebsd:~ # ifconfig em1 mtu 1600
root@freebsd:~ # ifconfig em1 mtu 1500

ospfd log file:

2018/01/11 10:16:55 OSPF: Zebra: Interface[em1] state update speed 1000 -> 1000, bw  0 -> 0
2018/01/11 10:16:56 OSPF: Zebra: Interface[em1] state update speed 1000 -> 1000, bw  0 -> 0
2018/01/11 10:16:56 OSPF: Zebra: Interface[em1] MTU change 1500 -> 1600.

2018/01/11 10:17:01 OSPF: Zebra: Interface[em1] state update speed 1000 -> 1000, bw  0 -> 0
2018/01/11 10:17:01 OSPF: Zebra: Interface[em1] MTU change 1600 -> 1500.

Please provide more details about the OS version you're using and if the problem is specific to PPP links or if it also happens for ethernet interfaces.

@nevzorofff
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nevzorofff commented Jan 12, 2018 via email

@bisdhdh
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bisdhdh commented Aug 9, 2018 •
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  @nevzorofff
 
I tried verifying this behaviour with two FRR virtual routers(running FRR master 5.2 ), connect via two different ip4 links. I had let the adjacency  come up in both the links.
 

R1(config)# do show ip ospf neighbor 
 
Neighbor ID     Pri State           Dead Time Address         Interface            RXmtL RqstL DBsmL
10.10.10.34       1 Full/Backup       34.199s 192.168.1.9     ens192:192.168.1.8       0     0     0
10.10.10.34       1 Full/DR           36.224s 10.10.10.34     ens224:10.10.10.33       0     0     0
 
 
R2(config)# do show ip ospf neighbor 
 
Neighbor ID     Pri State           Dead Time Address         Interface            RXmtL RqstL DBsmL
10.10.10.33       1 Full/DR           39.798s 192.168.1.8     ens192:192.168.1.9       0     0     0
10.10.10.33       1 Full/Backup       38.056s 10.10.10.33     ens224:10.10.10.34       0     0     0

 
  
After that I played with the MTU i.e changed it from 1500 -> 1600. I saw ospf at the other end could detect the change in MTU and adjacency was torn down.

root@R2:~# ifconfig ens192
ens192    Link encap:Ethernet  HWaddr 00:50:56:96:c1:6d  
          inet addr:192.168.1.9  Bcast:192.168.1.31  Mask:255.255.255.224
          inet6 addr: fe80::250:56ff:fe96:c16d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:96 errors:0 dropped:307 overruns:0 frame:0
          TX packets:46 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:8182 (8.1 KB)  TX bytes:3708 (3.7 KB)

 

root@R2:~# ifconfig ens192 mtu 1600
 
R2(config)# 
R2(config)# do show ip ospf neighbor 
 
Neighbor ID     Pri State           Dead Time Address         Interface            RXmtL RqstL DBsmL
10.10.10.33       1 ExStart/DR        37.704s 192.168.1.8     ens192:192.168.1.9       0     0     0
10.10.10.33       1 Full/Backup       39.642s 10.10.10.33     ens224:10.10.10.34       0     0     0

 

Aug  9 01:15:08 dev ospfd[31173]: Packet[DD]: Neighbor 10.10.10.34 MTU 1600 is larger than 
[ens192:192.168.1.8]'s MTU 1500
Aug  9 01:16:58 dev ospfd[31173]: message repeated 22 times: [ Packet[DD]: Neighbor 10.10.10.34 
MTU 1600 is larger than [ens192:192.168.1.8]'s MTU 1500]
Aug  9 01:17:01 dev CRON[31682]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Aug  9 01:17:03 dev ospfd[31173]: Packet[DD]: Neighbor 10.10.10.34 MTU 1600 is larger than [ens192:192.168.1.8]'s MTU 1500
 
R1(config)# 
R1(config)# do show ip ospf neighbor 
 
Neighbor ID     Pri State           Dead Time Address         Interface            RXmtL RqstL DBsmL
10.10.10.34       1 ExStart/Backup    35.062s 192.168.1.9     ens192:192.168.1.8       0     0     0
10.10.10.34       1 Full/DR           35.026s 10.10.10.34     ens224:10.10.10.33       0     0     0
 
R1(config)# 

Now changing the MTU back from 1600 to 1500 and the adjacency is back.

root@R2:~# ifconfig ens192 mtu 1500
 
 
R1(config)# Aug  9 01:18:48 dev ospfd[31173]: message repeated 21 times: [ Packet[DD]: Neighbor 
10.10.10.34 MTU 1600 is larger than [ens192:192.168.1.8]'s MTU 1500]
Aug  9 01:18:58 dev ospfd[31173]: SPF Processing Time(usecs): 101
Aug  9 01:18:58 dev ospfd[31173]: #011    SPF Time: 73
Aug  9 01:18:58 dev ospfd[31173]: #011   InterArea: 1
Aug  9 01:18:58 dev ospfd[31173]: #011       Prune: 1
Aug  9 01:18:58 dev ospfd[31173]: #011RouteInstall: 18

 
R1(config)# 
R1(config)# do show ip ospf neighbor 
 
Neighbor ID     Pri State           Dead Time Address         Interface            RXmtL RqstL DBsmL
10.10.10.34       1 Full/Backup       39.047s 192.168.1.9     ens192:192.168.1.8       0     0     0
10.10.10.34       1 Full/DR           33.494s 10.10.10.34     ens224:10.10.10.33       0     0     0

 
 

R1(config)# do show version 
FRRouting 5.1-dev-MyOwnFRRVersion-g06a5959 (R1).
Copyright 1996-2005 Kunihiro Ishiguro, et al.
This is a git build of frr-5.1-dev-320-g06a5959
Associated branch(es):
       local:master
       github/frrouting/frr.git/master
 
configured with:
     '--prefix=/usr' '--enable-exampledir=/usr/share/doc/frr/examples/' '--localstatedir=/var/run/frr' '--sbindir=/usr/lib/frr' '--sysconfdir=/etc/frr' '--enable-pimd' '--enable-watchfrr' '--enable-ospfclient=yes' '--enable-ospfapi=yes' '--enable-multipath=64' '--enable-user=frr' '--enable-group=frr' '--enable-vty-group=frrvty' '--enable-configfile-mask=0640' '--enable-logfile-mask=0640' '--enable-rtadv' '--enable-fpm' '--enable-systemd=yes' '--with-pkg-git-version' '--with-pkg-extra-version=-MyOwnFRRVersion'
R1(config)# exit
R1# 
R1# exit
root@dev:/var/log/frr# uname -a
Linux dev 4.4.36-nn3-server #nn3 SMP PREEMPT Thu Apr 13 08:23:18 PDT 2017 x86_64 x86_64 x86_64 GNU/Linux

 
 
Everything looks fine to me. Let me know if we are in the same page !

@qlyoung qlyoung added ospf question Not a bug labels Apr 17, 2019
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qlyoung commented Apr 17, 2019

Looks like it works, reopen if not

@qlyoung qlyoung closed this as completed Apr 17, 2019
@nevzorofff
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FreeBSD 12.2-RELEASE-p4 and frr7-7.5_1 — same problem

d# sh ip ospf interface
ng1 is up
ifindex 10, MTU 1500 bytes, BW 0 Mbit <UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST>

ifconfig:
ng1: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> metric 0 mtu 1400
inet 192.168.199.1 --> 192.168.199.5 netmask 0xffffffff
inet6 fe80::2e0:f4ff:fe1e:2839%ng1 prefixlen 64 scopeid 0xa
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>

@nevzorofff nevzorofff mentioned this issue Mar 13, 2021
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@rwestphal @qlyoung @bisdhdh @nevzorofff