[c-nsp] ASR 1k, 3.1.0S MTU issues on PortChannel interfaces

[Irina Arsenieva]

Hi there,
AFAIK, to change MTU on Po1.600, you have to change it on Po1, then Po1.600 
MTU = Po1 - 4
which makes sense as 802.1Q tag size is 4 bytes.
And I also suggest trying "clns mtu 1496" on both ends.
Rgds
Alex

--------------------------------------------------
From: "Pshem Kowalczyk" <pshem.k at gmail.com>
Sent: Wednesday, November 17, 2010 11:05 PM
To: <cisco-nsp at puck.nether.net>
Subject: [c-nsp] ASR 1k, 3.1.0S MTU issues on PortChannel interfaces

> Hi,
>
> I'm currently trying to test the following scenario:
>
> ASR1k ---- 4900M ----- ASR9k
>
> the 1k runs 3.1.0S (or 15.0(1)S)
> the 9k runs 3.9.1 (XR)
>
> as the link between the 4900M and 9k is provided by a third party we
> only have a MTU of 4400 there. There are 3 links between 1k and 4900M.
> I'm struggling with getting the ISIS to come up, as I suspect due to
> MTU on the PortChannel interface:
>
> Port-channel1 is up, line protocol is up
>  Hardware is GEChannel, address is 5475.d089.a4c0 (bia 5475.d089.a4c0)
>  MTU 4400 bytes, BW 30000000 Kbit/sec, DLY 10 usec,
> <-------------------------------------------
>     reliability 255/255, txload 1/255, rxload 1/255
>  Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set
>  Keepalive set (10 sec)
>  ARP type: ARPA, ARP Timeout 04:00:00
>    No. of active members in this channel: 3
>        Member 0 : TenGigabitEthernet0/0/0 , Full-duplex, 10000Mb/s
>        Member 1 : TenGigabitEthernet1/0/0 , Full-duplex, 10000Mb/s
>        Member 2 : TenGigabitEthernet2/0/0 , Full-duplex, 10000Mb/s
>    No. of PF_JUMBO supported members in this channel : 3
>
> interface Port-channel1
> mtu 4400
> no ip address
> end
>
> Port-channel1.600 is up, line protocol is up
>  Hardware is GEChannel, address is 5475.d089.a4c0 (bia 5475.d089.a4c0)
>  Description: SPNZSKY01
>  Internet address is 10.123.223.2/29
>  MTU 1500 bytes, BW 30000000 Kbit/sec, DLY 10 usec,
> <-------------------------------------------
>     reliability 255/255, txload 1/255, rxload 1/255
>  Encapsulation 802.1Q Virtual LAN, Vlan ID  600.
>
> interface Port-channel1.600
> description SPNZSKY01
> encapsulation dot1Q 600
> ip address 10.123.223.2 255.255.255.248
> ip mtu 4396
> ip router isis vfnz-core
> mpls ip
> isis network point-to-point
> isis authentication mode md5
> isis authentication key-chain VFNZ-KEY-CHAIN
> isis csnp-interval 10
>
> I tried multiple things already to change that MTU, but it just
> doesn't want to move (removing the config and re-applying it doesn't
> work either)
>
> when I debug isis adj I get the following:
>
> *Nov 17 15:50:46.998: ISIS-Adj: Sending serial IIH on
> Port-channel1.600, length 1496
>
>
> when I look on the 9k I can see:
> RP/0/RSP0/CPU0:Nov 18 11:57:19.616 : isis[285]: SEND P2P IIH (L2) on
> TenGigE0/0/0/1.600: Holdtime 30s, Length 4379
> RP/0/RSP0/CPU0:Nov 18 11:57:24.163 : isis[285]: RECV P2P IIH (L2) from
> TenGigE0/0/0/1.600 SNPA 5475.d089.a4c0: System ID BGAUESD01, Holdtime
> 30, length 1496
>
> I can not ping with anything bigger then 1500 from the 1K either.
>
> The 4900M has all interfaces set to MTU of 9196 (max for the platform).
>
> Any idea how to change that mtu?
>
> kind regards
> Pshem
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