Re: [OSPF] Increasing the maximum number of links advertisable in a single Router LSA

"Acee Lindem (acee)" <acee@cisco.com> Mon, 04 April 2016 13:56 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: Vlad Olariu <florinvlad.olariu@gmail.com>, "ospf@ietf.org" <ospf@ietf.org>
Thread-Topic: [OSPF] Increasing the maximum number of links advertisable in a single Router LSA
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Date: Mon, 4 Apr 2016 13:55:52 +0000
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Subject: Re: [OSPF] Increasing the maximum number of links advertisable in a single Router LSA
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Hi Vlad,

From: OSPF <ospf-bounces@ietf.org<mailto:ospf-bounces@ietf.org>> on behalf of Vlad Olariu <florinvlad.olariu@gmail.com<mailto:florinvlad.olariu@gmail.com>>
Date: Monday, April 4, 2016 at 8:27 AM
To: OSPF WG List <ospf@ietf.org<mailto:ospf@ietf.org>>
Subject: [OSPF] Increasing the maximum number of links advertisable in a single Router LSA

Hello All,

Considering what the OSPFv2 RFC states:

A.4.2 All of the router's links to the area must be described in a single router-LSA.

The maximum number of links advertisable in a single Router-LSA for a single LSA is around 5K.

Following this, I have two questions:
> How come the # links has 2 bytes, allowing for up to 65536 links?
> Is there any way to bypass the 5K limit?

No - this was fixed in OSPFv3 by supporting a variable number of Router-LSAs which are concatenated. This is yet another advantage of OSPFv3 over OSPFv2.

This has not been a problem heretofore and I know of several implementations that have lower Router-LSA link limits due to not supporting IP frag/reassembly up to 64K.

Thanks,
Acee




Thank you.

P.S This is of course just an exercise. I don't expect any sane network design to require that many links in the same area.