[c-nsp] IP MTU setting + OSPF

[Reuben Farrelly]

And don't forget - just in case this applies to you:

ip mtu 1500

does NOT apply to IPv6, you'll need to -explicitly- set "ipv6 mtu 1500" as 
well :-)

Reuben
(who recently found this out the hard way with IPv6 OSPF)


On 22/12/2009 7:08 PM, Mikael Abrahamsson wrote:
> On Mon, 21 Dec 2009, Chris Wopat wrote:
>
>> I'm changing MTU on some 7200s with PA-FE's to 1530 with the "mtu
>> 1530" command on the interface. To get OSPF to neighbor with a 2800
>> (no user settable MTU), I've put "ip mtu 1500" on the 7200. In my
>> testing this works fine. Does this in any way prevent the 7200 from
>> generating an OSPF packet that's larger than 1500 and potentially
>> breaking things down the road? The following links have been helpful
>> for MTU descriptions but I'm not seeing the answer to this question in
>> there.
>
> If you set "ip mtu 1500" then indeed it will not send any IP packets
> larger than 1500, and since OSPF runs over IP, this is also affected.
>
> But yes, you're doing the right thing (if the "mtu 1530" command is
> because you're running MPLS or something else non-IP that needs a higher
> MTU).
>