From: ccie2be (ccie2be@nyc.rr.com)
Date: Tue Jul 27 2004 - 10:56:15 GMT-3
This is from the book ISIS Network Design Solutions
****************************************
The no hello padding command is designed to prevent network bandwidth from
being wasted by the periodic exchange of hellos over interfaces with large
message transmission unit (MTU) sizes. The IS-IS protocol requires hellos to
be padded to the larger of the MTU or LSP buffer size.
This would technically guarantee that systems forming adjacencies over a
link can receive and process each others LSPs and other IS-IS packets over
the link. However, in practice, the same MTU size is used on the interfaces
of the connecting routers; therefore, padding hello packets is irrelevant in
most cases. The command disables the default behavior, resulting in
significant bandwidth savings, especially in situations where small hello
intervals have been configured and the MTU size is reasonably large.
A global router-level variant of this command provides options to
selectively disable padding on all IS-IS interfaces or all point-to-point
interfaces or all multipoint interfaces (see Example 9-24). You can use an
interface-level variant of the command for a single interface application,
as shown in Example 9-25.
Example 9-24 Disabling Hello Padding on Multiple Interfaces
RTA(config)#router isis
RTA(config-router)#no hello padding ?
multipoint Pad LAN hello PDUs
point-to-point Pad point-to-point hello PDUs
Example 9-25 Disabling Hello Padding on an Interface
RTA(config)#int pos 2/0
Rtr-A(config-if)#no isis hello paddingHTH, Tim
----- Original Message -----
From: "Kenneth Wygand" <KWygand@customonline.com>
To: "Geert Nijs" <geert.nijs@simac.be>; <ccielab@groupstudy.com>
Sent: Tuesday, July 27, 2004 8:48 AM
Subject: RE: ISIS Hello Padding
> Geert,
>
> What things need to match before an adjacency can form for ISIS? (Think
about this before continuing to read my email). Yes, MTU size is one, but
that's not the only one. ;-)
>
> If you are still stuck, try a "debug isis adjacency" to see why your
adjacency is not forming... the answer should jump out at you. :)
>
> By the way, you are correct in that disabling the "hello-padding" will
allow adjacencies to form independent of the MTU mismatch on both sides.
>
> Ken
>
> ________________________________
>
> From: nobody@groupstudy.com on behalf of Geert Nijs
> Sent: Tue 7/27/2004 3:58 AM
> To: ccielab@groupstudy.com
> Subject: ISIS Hello Padding
>
>
>
> Hi group,
>
> i just discovered the following command:
>
> (config-if)# no isis hello padding
>
> I can`t find anything about this command in the alfabetic key index on the
doc cd ???
>
>
> I was thinking that this command could maybe resolve an MTU mismatch on a
link, but i just
> configured a Frame Relay interface with a different MTU size on each side,
put this command on both
> sides, but adjacency still doesn`t come up. So what does it do exactly ?
>
>
> Regards,
>
> Geert
>
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