How to ignore OSPF MTU checking?
Is there a way to disable OSPF MTU checking? In Cisco the relevant command is 'ip ospf mtu-ignore'. Thanks, Kenth
On Mon, Mar 18, 2019 at 08:34:59AM +0000, Kenth Eriksson wrote:
Is there a way to disable OSPF MTU checking? In Cisco the relevant command is 'ip ospf mtu-ignore'.
We do not have that option. Would it be useful? For what cases is that necessary? -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."
On Mon, Mar 18, 2019 at 08:34:59AM +0000, Kenth Eriksson wrote:> Is there a way to disable OSPF MTU checking? In Cisco the relevant> command is 'ip ospf mtu-ignore'.>We do not have that option. Would it be useful? For what cases is thatnecessary?-- >Elen sila lumenn' omentielvoElen - Cisco switches require this for proper OSPF operation, if MTU is set different on equipment. But afaik it does not hit Bird. We have such sessions between Cisco and Bird. And works fine without this setting on Bird. But maybe therr is scenario we have never met but Kenth did?Best wishes,Peter
On Fri, Mar 22, 2019 at 09:24:58PM +0100, Piotr Marciniak wrote:
Cisco switches require this for proper OSPF operation, if MTU is set different on equipment. But afaik it does not hit Bird. We have such sessions between Cisco and Bird. And works fine without this setting on Bird. But maybe therr is scenario we have never met but Kenth did?Best wishes,Peter
We have a bug in older versions of BIRD that it does not verify that MTU of both sides is the same. We fixed that in the latest versions. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."
On Sun, 2019-03-24 at 04:13 +0100, Ondrej Zajicek wrote:
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On Fri, Mar 22, 2019 at 09:24:58PM +0100, Piotr Marciniak wrote:
Cisco switches require this for proper OSPF operation, if MTU is set different on equipment. But afaik it does not hit Bird. We have such sessions between Cisco and Bird. And works fine without this setting on Bird. But maybe therr is scenario we have never met but Kenth did?Best wishes,Peter
We have a bug in older versions of BIRD that it does not verify that MTU of both sides is the same. We fixed that in the latest versions.
How does bird handle transmission of OSPF packets packets larger than the link MTU? Does it rely on IP fragmentation? Or can it split into multiple protocol packets? What is the expected bird behaviour if the link mtu is different of the two sides?
-- Elen sila lumenn' omentielvo
Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."
On Mon, Mar 25, 2019 at 07:23:02AM +0000, Kenth Eriksson wrote:
On Fri, Mar 22, 2019 at 09:24:58PM +0100, Piotr Marciniak wrote:
Cisco switches require this for proper OSPF operation, if MTU is set different on equipment. But afaik it does not hit Bird. We have such sessions between Cisco and Bird. And works fine without this setting on Bird. But maybe therr is scenario we have never met but Kenth did?Best wishes,Peter
We have a bug in older versions of BIRD that it does not verify that MTU of both sides is the same. We fixed that in the latest versions.
How does bird handle transmission of OSPF packets packets larger than the link MTU? Does it rely on IP fragmentation? Or can it split into multiple protocol packets?
BIRD splits OSPF traffic to packets smaller than link MTU when possible. If it is not possible (e.g. one LSA larger that MTU), larger packet is used and we rely on OS to do fragmentation. We also suppose that OS assembles incoming packets transparently. AFAIK that happens in Linux, not sure about BSD.
What is the expected bird behaviour if the link mtu is different of the two sides?
Expected behavior (specified by OSPF RFC) is to forbid an association to be established. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."
participants (3)
-
Kenth Eriksson -
Ondrej Zajicek -
Piotr Marciniak