Eigrp stub routing

[Arun]

When you configure eigrp stub routing your neighbors shouldnt forward queries about the active routes to you. But as you know,query messages are sent to multicast address then how the stub router is excluded from the group.

[paul driver]

Hello

The stub router notify s its neighboring peers that its an eigrp stub  and so theses neighboring routers will receive that notification and will then not send queries to that stub.

res

Paul

[e.ciollaro · Accepted solution]

Hi,

I thnk that this feature is mainly used on WAN link that are not multiaccess.  In any case made a little lab (see attached figure).  I tried to sh R3 loopback configuring R2 as a stub network and as a normal EIGRP router. In the first case this is the debug output:

R2 as a stub router:

R3(config-if)#sh
R3(config-if)#
*Mar  1 00:53:59.207: DUAL: rcvupdate: 10.3.3.0/24 via Connected metric 4294967295/4294967295
*Mar  1 00:53:59.211: DUAL: Find FS for dest 10.3.3.0/24. FD is 128256, RD is 128256
*Mar  1 00:53:59.215: DUAL:     0.0.0.0 metric 4294967295/4294967295 not found Dmin is 4294967295
*Mar  1 00:53:59.219: DUAL: Peer total 2 stub 1 template 1                         note "stub 1"
*Mar  1 00:53:59.223: DUAL: Dest 10.3.3.0/24 entering active state.
*Mar  1 00:53:59.223: DUAL: Set reply-status table. Count is 1.                   R3 is waiting just 1 answer (2 neighbor but 1 of them is stub)
*Mar  1 00:53:59.227: DUAL: Not doing split horizon. Query stub suppressed
*Mar  1 00:53:59.355: DUAL: dest(10.3.3.0/24) active
*Mar  1 00:53:59.355: DUAL: rcvquery: 10.3.3.0/24 via 192.168.234.4 metric 4294967295/4294967295, RD is 4294967295
*Mar  1 00:53:59.359: DUAL: send REPLY(r1/n1) about 10.3.3.0/24 to 192.168.234.4
*Mar  1 00:53:59.371: EIGRP: Enqueueing REPLY on FastEthernet0/0 nbr 192.168.234.4 iidbQ un/rely 0/1 peerQ un/rely 0/0 serno 45-45
*Mar  1 00:53:59.387: EIGRP: Sending REPLY on FastEthernet0/0 nbr 192.168.234.4
*Mar  1 00:53:59.391:   AS 100, Flags 0x0, Seq 55/52 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/1 serno 45-45
*Mar  1 00:53:59.463: EIGRP: Received REPLY on FastEthernet0/0 nbr 192.168.234.4                         replay from R4
*Mar  1 00:53:59.463:   AS 100, Flags 0x0, Seq 53/55 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
*Mar  1 00:53:59.463: DUAL: rcvreply: 10.3.3.0/24 via 192.168.234.4 metric 4294967295/4294967295
*Mar  1 00:53:59.463: DUAL: reply count is 1
*Mar  1 00:53:59.467: DUAL: Clearing handle 1, count now 0                                                                no other replay pending
*Mar  1 00:53:59.467: DUAL: Freeing reply status table
*Mar  1 00:53:59.471: DUAL: Find FS for dest 10.3.3.0/24. FD is 4294967295, RD is 4294967295 found
*Mar  1 00:53:59.471: DUAL: Removing dest 10.3.3.0/24, nexthop 0.0.0.0, infosource 0.0.0.0                 flush route without an answer from R2
*Mar  1 00:53:59.471: DUAL: Removing dest 10.3.3.0/24, nexthop 192.168.234.4, infosource 192.168.234.4
*Mar  1 00:53:59.471: DUAL: Send update about 10.3.3.0/24.  Reason: rt gone
*Mar  1 00:53:59.471: DUAL: Send update about 10.3.3.0/24.  Reason: lost if
*Mar  1 00:53:59.575: DUAL: dest(10.3.3.0/24) not active
*Mar  1 00:53:59.579: DUAL: rcvquery: 10.3.3.0/24 via 192.168.234.2 metric 4294967295/4294967295, RD is 4294967295
*Mar  1 00:53:59.583: DUAL: send REPLY(r1/n1) about 10.3.3.0/24 to 192.168.234.2
*Mar  1 00:53:59.587: EIGRP: Enqueueing REPLY on FastEthernet0/0 nbr 192.168.234.2 iidbQ un/rely 0/1 peerQ un/rely 1/0 serno 47-47
*Mar  1 00:53:59.599: EIGRP: Sending REPLY on FastEthernet0/0 nbr 192.168.234.2
*Mar  1 00:53:59.603:   AS 100, Flags 0x0, Seq 57/48 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/1 serno 47-47
*Mar  1 00:53:59.683: DUAL: Removing dest 10.3.3.0/24, nexthop 192.168.234.2, infosource 192.168.234.2
*Mar  1 00:53:59.687: DUAL: No routes.  Flushing dest 10.3.3.0/24
*Mar  1 00:54:01.195: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down
*Mar  1 00:54:02.195: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down

Normal router

R3(config-if)#sh
R3(config-if)#
*Mar  1 00:52:23.679: DUAL: rcvupdate: 10.3.3.0/24 via Connected metric 4294967295/4294967295
*Mar  1 00:52:23.683: DUAL: Find FS for dest 10.3.3.0/24. FD is 128256, RD is 128256
*Mar  1 00:52:23.687: DUAL:     0.0.0.0 metric 4294967295/4294967295 not found Dmin is 4294967295
*Mar  1 00:52:23.691: DUAL: Peer total 2 stub 0 template 2                                                                       note stub 0 
*Mar  1 00:52:23.695: DUAL: Dest 10.3.3.0/24 entering active state.
*Mar  1 00:52:23.695: DUAL: Set reply-status table. Count is 2.                                                                 2 answer needed
*Mar  1 00:52:23.699: DUAL: Not doing split horizon
*Mar  1 00:52:23.815: EIGRP: Received REPLY on FastEthernet0/0 nbr 192.168.234.4                                 first answer (R4)
*Mar  1 00:52:23.815:   AS 100, Flags 0x0, Seq 45/47 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0
*Mar  1 00:52:23.819: DUAL: dest(10.3.3.0/24) active
*Mar  1 00:52:23.823: DUAL: rcvreply: 10.3.3.0/24 via 192.168.234.4 metric 4294967295/4294967295
*Mar  1 00:52:23.823: DUAL: reply count is 2
*Mar  1 00:52:23.827: DUAL: Clearing handle 1, count now 1                                                                     still one answer pending
*Mar  1 00:52:23.831: DUAL: Removing dest 10.3.3.0/24, nexthop 192.168.234.4, infosource 192.168.234.4

*Mar  1 00:52:23.843: EIGRP: Received REPLY on FastEthernet0/0 nbr 192.168.234.2                               2nd and last replay (in previous example on answer was received from R2)
*Mar  1 00:52:23.847:   AS 100, Flags 0x0, Seq 39/47 idbQ 0/0 iidbQ un/rely 0/0 peerQ un/rely 0/0

*Mar  1 00:52:23.851: DUAL: dest(10.3.3.0/24) active
*Mar  1 00:52:23.855: DUAL: rcvreply: 10.3.3.0/24 via 192.168.234.2 metric 4294967295/4294967295
*Mar  1 00:52:23.855: DUAL: reply count is 1
*Mar  1 00:52:23.855: DUAL: Clearing handle 0, count now 0                                                                no other replay pending
*Mar  1 00:52:23.859: DUAL: Freeing reply status table
*Mar  1 00:52:23.859: DUAL: Find FS for dest 10.3.3.0/24. FD is 4294967295, RD is 4294967295 found
*Mar  1 00:52:23.863: DUAL: Removing dest 10.3.3.0/24, nexthop 0.0.0.0, infosource 0.0.0.0                flushng router
*Mar  1 00:52:23.867: DUAL: Removing dest 10.3.3.0/24, nexthop 192.168.234.2, infosource 192.168.234.2
*Mar  1 00:52:23.871: DUAL: No routes.  Flushing dest 10.3.3.0/24                       
 

So the answer to your question "how the stub router is excluded from the group" is that it receives the query but the router sending the query doesn't requires a replay from stub router

[Arun]

Yep. i have seen this in my lab too.. captured the packets and found that the queries are actually forwarded to the stub routers.. but  cisco document explains this feature in a different way "Any neighbor that receives a packet informing it of the stub status will not query the stub router for any routes"   :) :)

[e.ciollaro]

I think that's because they suppose to be configured on WAN point-to-point or frame-relay links with just one  neighbor per link. In that case no query is generated.