eigrp topology table...

in the beginning, there was a topology table, and it passed on its data to neighbors...

r1#sh ip eigrp topo
EIGRP-IPv4 Topology Table for AS(1)/ID(10.1.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 2.2.2.0/24, 1 successors, FD is 2297856
        via 10.1.1.2 (2297856/128256), Serial1/0
P 3.3.3.0/24, 1 successors, FD is 2297856
        via 10.1.1.3 (2297856/128256), Serial1/0
P 1.1.1.0/24, 1 successors, FD is 128256
        via Connected, Loopback0
P 10.1.1.0/24, 1 successors, FD is 2169856
        via Connected, Serial1/0
P 4.4.4.0/24, 2 successors, FD is 2297856
        via 10.1.1.4 (2297856/128256), Serial1/0
        via 10.1.1.5 (2297856/128256), Serial1/0

for this network...

then cisco said something like this here:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f07.shtml#topology_table


The Topology Table is populated by the protocol dependent modules and acted upon by the DUAL finite state machine. It contains all destinations advertised by neighboring routers. Associated with each entry is the destination address and a list of neighbors that have advertised the destination. For each neighbor, the advertised metric is recorded. This is the metric that the neighbor stores in its routing table. If the neighbor is advertising this destination, it must be using the route to forward packets. This is an important rule that distance vector protocols must follow.
Also associated with the destination is the metric that the router uses to reach the destination. This is the sum of the best advertised metric from all neighbors plus the link cost to the best neighbor. This is the metric that the router uses in the routing table and to advertise to other routers.


that doesn't explain very much...

r1#sh ip route | ex L | in loop
    
Gateway of last resort is not set

      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        1.1.1.0/24 is directly connected, Loopback0
      2.0.0.0/24 is subnetted, 1 subnets
D        2.2.2.0 [90/2297856] via 10.1.1.2, 00:37:13, Serial1/0
      3.0.0.0/24 is subnetted, 1 subnets
D        3.3.3.0 [90/2297856] via 10.1.1.3, 00:38:37, Serial1/0
      4.0.0.0/24 is subnetted, 1 subnets
D        4.4.4.0 [90/2297856] via 10.1.1.5, 00:38:24, Serial1/0
                 [90/2297856] via 10.1.1.4, 00:38:24, Serial1/0
      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C        10.1.1.0/24 is directly connected, Serial1/0

ok...

eigrp can send some topology data to neighbors once it has topology data to share... good...

there are two ways it does this...

by using network commands that include the networks of it's connected interfaces...

and by propagating redistribution of other networks' data into it...

Serial1/0 is up, line protocol is up
  Hardware is M4T
  Internet address is 10.1.1.1/24
  MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation FRAME-RELAY, crc 16, loopback not set

mtu is not an integer metric (k value) that it supplies to neighbors... the five integers it supplies are highlighted in red...

in the above wireshark output the k values are 1 0 1 0 0, the so called default k values...

it is important to remember that the k values represent integers between 1-255 and DO NOT represent the output from the show interface command... further, the TOS bit, not represented in the packet capture is always zero...

and eigrp is known as a simple routing protocol, go figure...

joe astorino has an excellent discussion about all this here:
 http://blog.ipexpert.com/2010/03/03/eigrp-metric-k-values/