[c-nsp] shut interfaces become enabled for some secs while reloading

[Tassos Chatzithomaoglou]

just a note here....official answer from Cisco is :

"This is common to all interface and the problem is due to the IOS init code implementation...
...during reload time, it will consider them as new interface so to put them in shutdown mode we have
to include the 'no ip addr' instead of relying on the shut command".

interesting...this means at least 2 things:

1) you shouldn't keep a router with shut interfaces and identical config on your network
2) a shut interface is actually shut during a reload, only if it doesn't have an ip address

--
Tassos

Tassos Chatzithomaoglou wrote on 25/9/2008 1:08 μμ:
> Has anyone met the above problem?
> 
> I'm trying a 7200/G2 with 12.2(31)SB13 and i noticed that while 
> reloading it, the shuted interfaces come up for 2 secs, which is more 
> than enough time to send packets through them (having portfast enabled 
> on the switch port).
> 
> I guess the config is parsed sequentially, so if the "shutdown" command 
> follows the "ip address x.x.x.x" command (which they do when doing "sh 
> run"), ip connectivity is established first.
> 
> The problem with the above is that if you have to prepare a second 
> router having identical config with another one (keeping the interfaces 
> of the second router in the shutdown state), you end up having duplicate 
> ips for a while (in my case 2 secs) when reloading the second router. 
> This small time is more than enough to make the hell out of arp/mac 
> tables!!!
> 
> I know there are many ways to avoid all this mess (remove/change ips, 
> shut switch ports instead of router ports, etc), but i was mainly 
> wondering if all this is expected/normal behavior.
>