Re: Stupid checksum and next LSA begining question

["Naidu, Venkata" <[e-mail]>]

Erblich,

->         When given a "update packet with say 5 LSAs", and the
->         1st LSA in this packet has a checksum error, should
->         the rest of the LSAs in the update be attempted to be
->         processed?

  1. If you are talking about LSA checksum (which is Fletcher
     checksum).

     RFC 2328 page 142 section 13 says:
     . . .
     (1) Validate the LSA's LS checksum.  If the checksum turns out
         to be invalid, discard the LSA and get the next one from
         the Link State Update packet.
     . . .

  2. If you are talking about OSPF packet checksum

     RFC 2328 page 61 section 8.2 says:
     . . .
         The authentication procedure may also
         verify the checksum field in the OSPF packet header (which,
         when used, is set to the standard IP 16-bit one's complement
         checksum of the OSPF packet's contents after excluding the
         64-bit authentication field).  If the authentication
         procedure fails, the packet should be discarded.
     . . .

->         Note: If we have a checksum error, this means that the
->         length and the start of the next LSA COULD be wrong.
->
->         We could assume that checking the type of the next LSA
->         could be within a valid LSA type range, and still not
->         have the correct begining of the 2nd or 3rd ... LSAs.

  In such a case, OSPF packet checksum could be wrong. So, the
  whole OSPF packet will be discarded.

Venkata.