the basic question,about ip route command

dmifly.chuang · ‎08-25-2011

i am testing routing protocol redistribute,now i have a question.R1,R2 and R3 is direct connection of eachother. eigrp running on R2 and R3 . R1 has a loopback interface.R2 need a loopback route,so i use ip route command. when i use ip route ip_address 0.0.0.0 next_hop_address and network at eigrp session in R2,i can not show up in R3. when i change form,i use ip route ip_address 0.0.0.0 interface_name.then R3's route table has this route.

can somebody explain it for me?thanks you

TarasKotov · ‎08-25-2011

Can you show eigrp sections on R2 and R3? Also show exact ip route command you wrote on R2.

dmifly.chuang · ‎08-25-2011

R2:

R2#sh ip eigrp topology
EIGRP-IPv4 Topology Table for AS(1)/ID(192.168.5.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status

P 192.168.4.0/24, 1 successors, FD is 281600
        via Connected, Ethernet0/1
P 6.6.6.6/32, 1 successors, FD is 281600
        via Rstatic (281600/0)
P 192.168.5.0/24, 1 successors, FD is 281600
        via Connected, Ethernet0/0

router eigrp 1

network 6.6.6.6 0.0.0.0

network 192.168.4.2 0.0.0.0

network 192.168.5.0

no auto-summary

ip route 6.6.6.6 255.255.255.255 Ethernet0/0

R3:

R3#sh ip eigrp topology
EIGRP-IPv4 Topology Table for AS(1)/ID(192.168.4.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status

P 192.168.4.0/24, 1 successors, FD is 281600
        via Connected, Ethernet0/1
P 6.6.6.6/32, 1 successors, FD is 307200
        via 192.168.4.2 (307200/281600), Ethernet0/1
P 192.168.5.0/24, 1 successors, FD is 307200
        via 192.168.4.2 (307200/281600), Ethernet0/1

TarasKotov · ‎08-25-2011

Show the output from show ip route on R2.

As I understand, static routes with interface as destination defined are treated as connected. That is why when you use network command under router eigrp 1 subsection, this route (6.6.6.6/32) is propagated through EIGRP domain:

CISCO2811(config)#ip route 6.6.6.6 255.255.255.255 fa0/1.100

CISCO2811#sh ip route static
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override
Gateway of last resort is 10.105.99.3 to network 0.0.0.0
      6.0.0.0/32 is subnetted, 1 subnets
S        6.6.6.6 is directly connected, FastEthernet0/1.100
      10.0.0.0/8 is variably subnetted, 34 subnets, 5 masks
S        10.105.0.0/16 is directly connected, Null0
S        10.105.12.0/24 [1/0] via 10.105.99.3
S        10.105.200.0/24 is directly connected, Null0
      172.16.0.0/27 is subnetted, 1 subnets
S        172.16.64.96 [1/0] via 172.30.0.169

As you see, Cisco treats 6.6.6.6/32 route as static, but it has zero (0) metric.

Also I want to notice that it's bad idea to use interface as destination for static route on broadcast interface. You can have problems with CPU load, packets drops or other bad network behavior.