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ISIS Adj not coming up

atif-siddiqui
Level 1
Level 1

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.

29 Replies 29

Harold Ritter
Cisco Employee
Cisco Employee

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,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

ok I see. I will try to find out. as it is WAN link provided by other provider.

thanks.

Another doubt I have is if after applying the mtu changes you shut/no shut both interfaces or just one.

Regards,

Antonio

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

On both sides issue a "show ip interface check the IP MTU value on each side.

Set the ISIS MTU on each respective interface to the IP MTU you observe and the adjacency will come up.

HTH-Cheers,

Swaroop

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

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

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,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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.

also if we have everything label switched is it necessary to set ip mtu?

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

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

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

Here is the debug from one side:

gigi 0/0/9 is the one that does not come up:

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