"unsupported" features in IOS ("mpls mtu") (was: Re: [c-nsp] High Availability PoP Design)

[Johannes Resch]

hi rodney,

On Fri, November 4, 2005 20:06, Rodney Dunn said:
> On Fri, Nov 04, 2005 at 07:44:41PM +0100, Gert Doering wrote:
>> hi,
>>
>> On Fri, Nov 04, 2005 at 12:31:21PM -0500, Rodney Dunn wrote:
>> > We support 1500 byte ip headers on those PA's +
>> > 6 labels (24) bytes.
>>
>> So if I understand this correctly, "mpls mtu 1524" will still work on
>> FE ports on 7200?
>
> Yes.

maybe you could comment on the output below? you may also want to read
case SR #602143087, which is directly related to the problem.

disclaimer: I know that this is from an unsupported engineering image. but
after opening a case with CTAC, they confirmed (see TAC case notes) that
this behaviour will stay in subsequent official 12.2S releases, and will
also be introduced in other trains (12.3).

I'd appreciate to hear your view on this, maybe there has been some
misunderstanding.

Router#sh run int f1/0
Building configuration...

Current configuration : 105 bytes
!
interface FastEthernet1/0
 ip address 192.168.0.1 255.255.255.0
 duplex full
 no clns route-cache
end

Router#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#int f1/0
Router(config-if)#mpls mtu 1508
% Please increase interface mtu to 1508 and then set mpls mtu


Router#sh ver
Cisco IOS Software, 7200 Software (C7200-P-M), Experimental Version
12.2(200508]
Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Fri 16-Sep-05 12:49 by sheroork

ROM: System Bootstrap, Version 12.1(20000710:044039) [nlaw-121E_npeb 117],
DEVEE
BOOTLDR: 7200 Software (C7200-BOOT-M), Version 12.0(24)S, EARLY DEPLOYMENT
RELE)

 Router uptime is 4 minutes
System returned to ROM by reload at 06:10:15 UTC Mon Nov 7 2005
System image file is "disk1:c7200-p-mz.15thsept"

Cisco 7206VXR (NPE400) processor (revision A) with 491520K/32768K bytes of
memo.
Processor board ID 30468560
R7000 CPU at 350Mhz, Implementation 39, Rev 3.2, 256KB L2 Cache
6 slot VXR midplane, Version 2.7


best regards,
-jr