Vivek,

>Since mtu depend on the type of network, it will be standard.
>So why go for such a check at ospf level.

MTU can be configureable for certain networks. If the datalink layer does
not negotiate it, it may cause problems at the OSPF layer. GigE also allows
non-standard jumbograms I think(so you cant always say that MTU is constant
for a particular link type).

This is one link I found
http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0008&L=OSPF&P=R2452

Thanks,
Vishwas

-----Original Message-----
From: Mailing List [mailto:OSPFdiscuss.microsoft.com]On Behalf Of
Manral, Vishwas
Sent: Friday, 25 January 2002 11:20 PM
To: OSPFdiscuss.microsoft.com
Subject: Re: Database Describtion Fragmentation!!

Amit,

The following links explain it better.

http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0008&L=OSPF&P=R2394

http://discuss.microsoft.com/SCRIPTS/WA-MSD.EXE?A2=ind0008&L=OSPF&P=R2279

-Vishwas

-----Original Message-----
From: Manral, Vishwas [mailto:VishwasMNETPLANE.COM]
Sent: Friday, January 25, 2002 10:37 PM
To: OSPFDISCUSS.MICROSOFT.COM
Subject: Re: Database Describtion Fragmentation!!

Amit,

>From RFC2328
        If the Interface MTU field in the Database Description packet
        indicates an IP datagram size that is larger than the router can
        accept on the receiving interface without fragmentation, the
        Database Description packet is rejected.

This is probably because OSPF has no method of fragmentation and relies on
IP for fragmentation. In case a an LSU is sent which is bigger than MTU, it
can be dropped, causing problems in the routing table. This is why I think,
DB description packets are used to convey Interface MTU(and are dropped in
case of a mismatch). Mind you, Interface MTU over virtual links is set to be
0.

Maybe John/Alex will explain it better.

Thanks,
Vishwas

-----Original Message-----
From: Amit Srivastava [mailto:amit_ospfYAHOO.COM]
Sent: Thursday, January 24, 2002 2:43 PM
To: OSPFDISCUSS.MICROSOFT.COM
Subject: Database Describtion Fragmentation!!

Hi All,
      Why is that the database describtion packets if
received after fragmentation is discarded!!
regards
Amit

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