EIGRP stub with leak map
Stub network in EIRG helps to reduce the Query propagation.
To understands the Query boundary; we have added a new router to the topology, R8. R8 as only a single connection to the EIGRP domain which is via R3.
We will shut down the interface containing 1.1.1.1/32 and see that R3 will send the query to R8 for the network that just went down.. We will use Wireshark to analyze the Query message R3 will send to R8, for example.
1 - EIGRP configuration in R8.
router eigrp 1
network 8.8.8.8 0.0.0.0
network 10.3.8.8 0.0.0.0
network 192.8.0.0 0.0.255.255
2 - Interface containing 1.1.1.1/32 subnet shutdown.
R1#conf t
R1(config)#int lo0
R1(config-if)#shut
R3 packet capture from the interface connecting to R8, show that query was sent to multicast IP address 224.0.0.10 and R8 replied to the packet.
R8 Reply packet capture output.
Now, we will configure R8 as stub router.
R8#conf t
R8(config)#router eigrp 1
R8(config-router)#eigrp stub
From R3 we can confirm that R8 is a stub by looking into the neighbor details.
R3#sho ip eigrp neighbors detail gigabitEthernet 3
EIGRP-IPv4 Neighbors for AS(1)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
2 10.3.8.8 Gi3 14 00:02:29 2 100 0 22
Version 25.0/2.0, Retrans: 0, Retries: 0, Prefixes: 3
Topology-ids from peer - 0
Topologies advertised to peer: base
Stub Peer Advertising (CONNECTED SUMMARY ) Routes
Suppressing queries
Max Nbrs: 0, Current Nbrs: 0
R3#
R1 interface has been unshut again, now we will capture again the packet and see the behavior.
R3 send an update to R8 informing about the prefix unavailability. This time, there was no query sent from R3 to R8
R8 just ack the packet from R3.
R7 also has only one path to the EIGRP domain and it is running the named mode. Below is the configuration of R7 as stub for both Ipv4 and IPv6.
R7#conf t
R7(config)#router eigrp CORE
R7(config-router)#address-family ipv4 autonomous-system 1
R7(config-router-af)#eigrp stub
R7(config-router-af)#address-family ipv6 autonomous-system 1
R7(config-router-af)#eigrp stub
Verification from R4, the upstream for R7 showing that R7 has been configured as stub.
IPv4 Neighbor
R4#sho ip eigrp neighbors detail gigabitEthernet 3
EIGRP-IPv4 VR(CORE) Address-Family Neighbors for AS(1)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
2 10.4.7.7 Gi3 13 02:24:38 1 100 0 18
Version 25.0/2.0, Retrans: 1, Retries: 0, Prefixes: 2
Topology-ids from peer - 0
Topologies advertised to peer: base
Stub Peer Advertising (CONNECTED SUMMARY ) Routes
Suppressing queries
Max Nbrs: 0, Current Nbrs: 0
IPv6 Neighbor
R4#sho ipv6 eigrp neighbors detail gigabitEthernet 3
EIGRP-IPv6 VR(CORE) Address-Family Neighbors for AS(1)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
2 Link-local address: Gi3 12 02:24:33 1 100 0 8
FE80::5224:75FF:FE02:800
Version 25.0/2.0, Retrans: 1, Retries: 0, Prefixes: 3
Topology-ids from peer - 0
Topologies advertised to peer: base
Stub Peer Advertising (CONNECTED SUMMARY ) Routes
Suppressing queries
Max Nbrs: 0, Current Nbrs: 0
Secondary component.
As per the show EIGRP neighbor details, we can see that the stub peer is advertising CONNECTED and SUMMARY only. This is the default behavir, even if not specifying it in the EIGRP configuration.
Below is the current configuration of EIGRP on R8. Note that connected and summary have been automatically added to the configuration.
router eigrp 1
network 8.8.8.8 0.0.0.0
network 10.3.8.8 0.0.0.0
network 192.8.0.0 0.0.255.255
redistribute connected
redistribute ospf 1 metric 1000000 10 255 1 1500
eigrp stub connected summary
We have added an OSPF link between R8 and ISP. R8 is doing mutual redistribution. Since R8 is stub, the routers learned from OSPF neighbor are not being observed inside the EIGRP domain. Below is an output of R8 and R3 showing that some prefixes are in R8 and not R3 and the rest of the EIGRP domain. 6.6.6.6 is a prefix located inside ISP.
R8#sho ip route ospf | in 6.6.6
O 6.6.6.6 [110/2] via 10.6.8.6, 00:06:26, GigabitEthernet2
From the output of R3, we can see that route to prefix 6.6.6.6 is missing. There is also a prefix 80.80.80.80 which belongs to R8, but it is being received because even though R8 is redistribuiting this subnet, it is still a connected subnet to R8
R3#sh ip route | in 10.3.8.8
D 8.8.8.8 [90/130816] via 10.3.8.8, 00:25:55, GigabitEthernet3
D EX 10.6.8.0/24 [170/3072] via 10.3.8.8, 00:25:55, GigabitEthernet3
D EX 80.80.80.80 [170/130816] via 10.3.8.8, 00:25:55, GigabitEthernet3
D 192.8.0.0/16 [90/130816] via 10.3.8.8, 00:25:55, GigabitEthernet3
Changing the Stub configuration.
There are several options on what to be advertised by the Stub router. See below for an example.
R8#conf t
R8(config)#router eigrp 1
R8(config-router)#eigrp stub ?
connected Do advertise connected routes
leak-map Allow dynamic prefixes based on the leak-map
receive-only Set receive only neighbor
redistributed Do advertise redistributed routes
static Do advertise static routes
summary Do advertise summary routes
<cr> <cr>
We will change the configuration on R8 to just allow the advertisement of the connected only subnets.
R8#conf t
R8(config)#router eig 1
R8(config-router)#eigrp stub summary
As we can see from the output of R3, only summary route is being advertised by R8.
R3#sh ip route | in 10.3.8.8
D 192.8.0.0/16 [90/130816] via 10.3.8.8, 00:01:22, GigabitEthernet3
R3#sho ip eigrp nei detail g3
EIGRP-IPv4 Neighbors for AS(1)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
2 10.3.8.8 Gi3 14 00:01:33 1 100 0 44
Version 25.0/2.0, Retrans: 0, Retries: 0, Prefixes: 1
Topology-ids from peer - 0
Topologies advertised to peer: base
Stub Peer Advertising (SUMMARY ) Routes
Suppressing queries
Max Nbrs: 0, Current Nbrs: 0
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