From: SUBSCRIBE OSPF Anonymous <[email-masked]>
Date: Fri, 16 Aug 2002 10:11:15 -0500

Hi,

Before I start my question, my Thanks to all, who did listen to my earlier question and trying to get back to me with ideas!
I really appreciate all your time and effort.

Well, I have one more question when OSPF establish adjacency with its neighbors.

During that period, I try to act my Simulator as Master and let OSPF Route be slave and while trying to establish an adjacency with OSPF Router, I am trying to send the below mentioned packet during DD packet exchange.

But, for some reason, OSPF router could not form an adjacency when I send these packets and stops at exChange state

i.e. OSPF Router and Simulator understands Master Slave relationship
OSPF Router sends DD packet with master sequence number and also sends LSA Header for (routerLSA)

I have few questions and any suggestions from your end is welcome and will be a big relief.

        * While looking at the packets, I am not sure how to calculate the checksum for LSA Header. I was under the impression that I should exclude Link State Age while performing checksum, but still not sure what I am missing here ...
        * Even though, LSA Header only contains 20 bytes, I noticed we always try to specify Packet Length has 36 bytes. Any reasons!?
        * Also, when I monitor my network, I notice for the packets only information upto Data Description and don't see LSA Header info.

Thanks and have a wonderful evening!

- G

Data Description Packet Information:

// ----- OSPF DD Ack Packet -----
//

//
// ----- Ethernet II -----
//

define ospf [ 00 20 9c 23 bc 70
        08 00 20 ac 9d d5
        08 00

//
// ----- Internet Protocol -----
// ----- 20 bytes -----

45
00
00 34                     // Total Length
5a a0                     // Identification
00                        // Flags
00                        // Frame Offset
40                        // TTL
59                        // Protocol (OSPF)
00 00                     // Checksum
0a 65 01 43               // Source
0a 65 01 41               // Destination

//
// ----- OSPF Header -----
//

02                        // OSPF Version
02                        // OSPF Packet Type (Hello Pkt)
00 34                     // Packet Length
0a 65 01 43                // Source OSPF Router ID
0a 65 01 40                        // Area ID
00 00                     // Packet Checksum
00 00                     // Auth Type (None)
00 00 00 00               // Auth Date (None)
00 00 00 00

//
// ----- OSPF Data Description Info -----
//

05 dc                     // Interface MTU
02                        // OSPF Version
00                        // Master
00 00 00 02              // DD Sequence

//
// ----- OSPF DD w/ LSA Header -------- 64 BYTES
//
01 88                   // LS Age 392 seconds
02                              // Options
01                              // Router LSA
0a 65 01 43             // Link State ID
0a 65 01 43             // Adv. Router
00 00 01 00             // LS Sequence Number
0a 02                   // Checksum
00 24                   // Length
];

xsum ospf[24] 14 20;
xsum ospf[46] 34 52;
// -xsum ospf[82] 66 28; - Checksum for LSA Header

send ospf;