10-13-2007 12:26 AM
I changed the MTU of my gige link from 1500 to 1600, and configured mpls MTU 1538. doing that ISIS does not form adj.
I see CLNS is showing neigbor but as ES-IS? why is that.
Router A:
interface GigabitEthernet0/0/9
description link to RouterB
mtu 1600
ip address x.x.x.x y.y.y.y
no ip directed-broadcast
ip router isis
no negotiation auto
tag-switching mtu 1538
tag-switching ip
isis network point-to-point
isis authentication mode md5
isis authentication key-chain KEY-ISIS
end
Router A neigbor:
RouterA#sh clns neighbors
System Id Interface SNPA State HT Type Protocol
RouterB(P-TGi0/0/9 001a.e3a2.8808 Up 292 IS ES-IS
Other end:
Router B:
interface GigabitEthernet0/0/8
description Connected to Router A
Gig0/0/9
mtu 1600
ip address x.x.x.x y.y.y.y
no ip directed-broadcast
ip router isis
no negotiation auto
tag-switching mtu 1538
tag-switching ip
isis network point-to-point
isis authentication mode md5
isis authentication key-chain KEY-ISIS
end
RouterA(P-EGi0/0/8 001b.2b04.ec09 Up 250 IS ES-IS
I cannot see ISIS neigbor here.
10-13-2007 08:35 AM
Atif,
The IS-IS hellos are probably not getting across the link. The reason you are seeing the adjacency as ES-IS is that the ES-IS hellos are not padded, while the IS-IS hellos are.
Do you have a switch between the two routers? If so, make sure that the switch allows 1600 bytes packets through.
Hope this helps,
10-13-2007 10:35 AM
ok I see. I will try to find out. as it is WAN link provided by other provider.
thanks.
10-14-2007 12:13 PM
Another doubt I have is if after applying the mtu changes you shut/no shut both interfaces or just one.
Regards,
Antonio
10-14-2007 08:01 PM
We did that, but did not work.
I will find out tomorrow what do we have in the middle...
If it is DWDM, will it affect us? is there MTU setting on it? I am not sure
10-14-2007 08:46 PM
On both sides issue a "show ip interface
Set the ISIS MTU on each respective interface to the IP MTU you observe and the adjacency will come up.
HTH-Cheers,
Swaroop
10-15-2007 06:48 PM
I agree with swaroop, this is due to the default hello padding, try disabling hello packet, if you are sure the both end point's MTU, this will reduce the CPU/BW. go into each interface and type
no isis hello padding
10-16-2007 05:56 AM
i did disable the padding, still does not come up.
only comes up when we reduce MTU to 1500. in the middle there is DWDM, which has enough limit for MTU
10-16-2007 04:36 PM
Atif,
It would definitely be worth pinging from one router to the other using packet sizes over 1500 bytes just to confirm your providers setting.
Regards,
10-16-2007 05:54 AM
GigabitEthernet0/0/9 is up, line protocol is up
Internet address is x.x.x.x/30
Broadcast address is 255.255.255.255
Address determined by non-volatile memory
MTU is 1600 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.2
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
ICMP redirects are always sent
ICMP unreachables are always sent
ICMP mask replies are never sent
IP fast switching is disabled
IP fast switching on the same interface is disabled
IP Flow switching is disabled
IP CEF switching is enabled
IP Null turbo vector
IP multicast fast switching is enabled
IP multicast distributed fast switching is disabled
IP route-cache flags are Fast, Distributed, CEF
Router Discovery is disabled
IP output packet accounting is disabled
IP access violation accounting is disabled
TCP/IP header compression is disabled
RTP/IP header compression is disabled
Probe proxy name replies are disabled
Policy routing is disabled
Network address translation is disabled
WCCP Redirect outbound is disabled
WCCP Redirect inbound is disabled
WCCP Redirect exclude is disabled
BGP Policy Mapping is disabled
Interface config:
mtu 1600
ip address x.x.x.x 255.255.255.252
no ip directed-broadcast
ip router isis NRP
no negotiation auto
tag-switching mtu 1538
tag-switching ip
isis network point-to-point
isis authentication mode md5
isis authentication key-chain KEY-ISIS
no isis hello padding
end
this is the same config on the other side.
10-16-2007 07:49 AM
also if we have everything label switched is it necessary to set ip mtu?
10-16-2007 04:18 AM
hello
alternatively, you can decrease 'clns mtu' on your interface. But as you will apparently run MPLS on the link, it's worth checking the link 'real mtu'
regards
Etienne
10-16-2007 08:22 AM
Your config looks fine, can you run debug isis adj-pac and attach the o/p. this shouldprovide a clue whats going wrong.
HTH-Cheers,
Swaroop
10-16-2007 08:28 AM
To add more, my initial reply was based on similar experience, but between 76k and GSR-IOS XR. But did a quick test with 76k and dont see any problem neither am able to introduce such problem with similar config.
HTH-Cheers,
Swaroop
10-16-2007 09:39 AM
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