EIGRP flushing default route

[Daniel Freitas]

Hi for all!

I have a weird scenario on my network. I have a Cat 6880 as a core of a site. This switch is connected to two 2921 that are connected with two different MPLS providers. On the border routers I'm injecting the full routing table of the site to the MPLS and injecting back on the EIGRP just the default route. The main issue that I am facing on this scenario is that when one provider comes down, on the core of the network both default routes are reset and I face some minutes outage until the network is able to re-converge. Any thoughts why this is happening?

Thanks in advance,

Daniel Freitas

CCIE SP

[chrihussey]

Could you provide details on the connectivity and L3 routing between the 2921s and the 6880 as well as how the default route is propogated? A diagram might be helpful too.

[Daniel Freitas]

Hello chrihussey!

Attaching here the topology and the BGP/EIGRP configuration of the whole site.

Thanks in advance for the help!

[Julio E. Moisa]

Hi,

Please check if Router 2 is not preferring the default route through the Core. 

[chrihussey]

It is always challenging to redistibute the same route into an IGP at different points on a network. In your case it is the default route. That is because one end will eventually see the others in the IGP and not inject their route as a result.  When ISP 1 fails, it needs to withdraw the route from BGP and then stop the redistribution into EIGRP. The 2921 to ISP 2, then needs to see the default route withdraw from EIGRP before it then redistributes its default route into EIGRP.

Other may have ideas, but if you configure IBGP between the 2921s and the 6880 and redistribute the ISP learned default route into EIGRP at the 6880 you would probably get better performance.

Hope this makes sense.

[Julio E. Moisa]

Hi Daniel,

Have you verified on the core if there is a feasible successor on the core? it looks like the Edge router 2 is preferring the default route from the Edge router 1 instead the learned through its ISP. Is possible to see the routing table and eigrp topology table just including the default route?

[Daniel Freitas]

This is not the case. The VSS is performing the equal cost load balance to the default route:

#sh ip route
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
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is 10.55.43.41 to network 0.0.0.0

D*EX  0.0.0.0/0 [170/15360] via 10.55.43.41, 1d19h, TenGigabitEthernet2/1/1
                [170/15360] via 10.55.43.37, 1d19h, TenGigabitEthernet1/1/1
      10.0.0.0/8 is variably subnetted, 36 subnets, 6 masks
D        10.55.25.16/28 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.25.80/28 [90/10368] via 10.55.43.45, 12:09:36, Port-channel18
D        10.55.26.64/26 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.26.192/26 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
D        10.55.32.0/24 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.33.0/24 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.34.0/24 [90/10368] via 10.55.43.58, 7w0d, Port-channel20

[Julio E. Moisa]

Is it the Core switch? could you please provide the show ip route and show ip eigrp top from Router 1 and 2?

Thank you in advance. 

[Daniel Freitas]

BR06-SW-CORE-01#sh ip route
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
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is 10.55.43.41 to network 0.0.0.0

D*EX  0.0.0.0/0 [170/15360] via 10.55.43.41, 1d21h, TenGigabitEthernet2/1/1
                [170/15360] via 10.55.43.37, 1d21h, TenGigabitEthernet1/1/1
      10.0.0.0/8 is variably subnetted, 36 subnets, 6 masks
D        10.55.25.16/28 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.25.80/28 [90/10368] via 10.55.43.45, 14:45:01, Port-channel18
D        10.55.26.64/26 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.26.192/26 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
D        10.55.32.0/24 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.33.0/24 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.34.0/24 [90/10368] via 10.55.43.58, 7w0d, Port-channel20
D        10.55.38.0/26 [90/10368] via 10.55.43.58, 2d03h, Port-channel20
D        10.55.38.64/26 [90/10368] via 10.55.43.58, 6w1d, Port-channel20
D        10.55.38.128/27 [90/10368] via 10.55.43.33, 4w5d, Port-channel19
D        10.55.38.192/26 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.40.0/24 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
D        10.55.41.0/24 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
D        10.55.42.0/24 [90/10368] via 10.55.43.58, 7w0d, Port-channel20
D        10.55.43.0/27 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
C        10.55.43.32/30 is directly connected, Port-channel19
L        10.55.43.34/32 is directly connected, Port-channel19
C        10.55.43.36/30 is directly connected, TenGigabitEthernet1/1/1
L        10.55.43.38/32 is directly connected, TenGigabitEthernet1/1/1
C        10.55.43.40/30 is directly connected, TenGigabitEthernet2/1/1
L        10.55.43.42/32 is directly connected, TenGigabitEthernet2/1/1
C        10.55.43.44/30 is directly connected, Port-channel18
L        10.55.43.46/32 is directly connected, Port-channel18
D        10.55.43.51/32
           [90/10880] via 10.55.43.37, 5d00h, TenGigabitEthernet1/1/1
D        10.55.43.52/32
           [90/10880] via 10.55.43.41, 5d00h, TenGigabitEthernet2/1/1
C        10.55.43.56/30 is directly connected, Port-channel20
L        10.55.43.57/32 is directly connected, Port-channel20
D        10.55.43.64/27 [90/10368] via 10.55.43.58, 6w5d, Port-channel20
D        10.55.43.96/27 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
D        10.55.46.32/27 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.46.64/27 [90/10368] via 10.55.43.58, 7w0d, Port-channel20
C        10.55.46.97/32 is directly connected, Loopback0
D        10.55.46.100/32
           [90/10880] via 10.55.43.37, 5d00h, TenGigabitEthernet1/1/1
D        10.55.46.101/32
           [90/10880] via 10.55.43.41, 5d00h, TenGigabitEthernet2/1/1
D        10.55.47.128/27 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.48.68/30
           [90/107520] via 10.55.43.37, 5d00h, TenGigabitEthernet1/1/1

BR06-SW-CORE-01#sh ip eigrp topology
EIGRP-IPv4 VR(LOGICALIS) Topology Table for AS(65006)/ID(10.55.43.97)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.55.46.32/27, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 10.55.43.52/32, 1 successors, FD is 1392640
        via 10.55.43.41 (1392640/163840), TenGigabitEthernet2/1/1
P 10.55.34.0/24, 1 successors, FD is 1327104
        via 10.55.43.58 (1327104/1310720), Port-channel20
P 10.55.46.100/32, 1 successors, FD is 1392640
        via 10.55.43.37 (1392640/163840), TenGigabitEthernet1/1/1
P 10.55.46.97/32, 1 successors, FD is 163840
        via Connected, Loopback0
P 10.55.38.0/26, 1 successors, FD is 1327104
        via 10.55.43.58 (1327104/1310720), Port-channel20
P 10.55.38.64/26, 1 successors, FD is 1327104
        via 10.55.43.58 (1327104/1310720), Port-channel20
P 10.55.38.192/26, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 10.55.43.64/27, 1 successors, FD is 1327104
        via 10.55.43.58 (1327104/1310720), Port-channel20
P 10.55.43.96/27, 1 successors, FD is 1327104
        via 10.55.43.45 (1327104/1310720), Port-channel18
P 10.55.42.0/24, 1 successors, FD is 1327104
        via 10.55.43.58 (1327104/1310720), Port-channel20
P 10.55.43.44/30, 1 successors, FD is 32768
        via Connected, Port-channel18
P 10.55.43.0/27, 1 successors, FD is 1327104
        via 10.55.43.45 (1327104/1310720), Port-channel18
P 10.55.32.0/24, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 10.55.40.0/24, 1 successors, FD is 1327104
        via 10.55.43.45 (1327104/1310720), Port-channel18
P 10.55.43.40/30, 1 successors, FD is 1310720
        via Connected, TenGigabitEthernet2/1/1
P 10.55.26.64/26, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 10.55.48.68/30, 1 successors, FD is 13762560
        via 10.55.43.37 (13762560/13107200), TenGigabitEthernet1/1/1
P 10.55.25.80/28, 1 successors, FD is 1327104
        via 10.55.43.45 (1327104/1310720), Port-channel18
P 10.55.47.128/27, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 10.55.25.16/28, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 0.0.0.0/0, 2 successors, FD is 1966080, tag is 18881
        via 10.55.43.37 (1966080/1310720), TenGigabitEthernet1/1/1
        via 10.55.43.41 (1966080/1310720), TenGigabitEthernet2/1/1
P 10.55.26.192/26, 1 successors, FD is 1327104
        via 10.55.43.45 (1327104/1310720), Port-channel18
P 10.55.41.0/24, 1 successors, FD is 1327104
        via 10.55.43.45 (1327104/1310720), Port-channel18
P 10.55.46.101/32, 1 successors, FD is 1392640
        via 10.55.43.41 (1392640/163840), TenGigabitEthernet2/1/1
P 10.55.43.56/30, 1 successors, FD is 32768
        via Connected, Port-channel20
P 10.55.43.32/30, 1 successors, FD is 32768
        via Connected, Port-channel19
P 10.55.43.36/30, 1 successors, FD is 1310720
        via Connected, TenGigabitEthernet1/1/1
P 10.55.33.0/24, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19
P 10.55.46.64/27, 1 successors, FD is 1327104
        via 10.55.43.58 (1327104/1310720), Port-channel20
P 10.55.43.51/32, 1 successors, FD is 1392640
        via 10.55.43.37 (1392640/163840), TenGigabitEthernet1/1/1
P 10.55.38.128/27, 1 successors, FD is 1327104
        via 10.55.43.33 (1327104/1310720), Port-channel19

BR06-SW-CORE-01#

[Daniel Freitas]

This is one output from when the one MPLS link had failed, about 2 days ago:

BR06-SW-CORE-01#sh ip route
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
       a - application route
       + - replicated route, % - next hop override

Gateway of last resort is 10.55.43.37 to network 0.0.0.0

D*EX  0.0.0.0/0 [170/15360] via 10.55.43.37, 00:33:14, TenGigabitEthernet1/1/1
      10.0.0.0/8 is variably subnetted, 36 subnets, 6 masks
D        10.55.25.16/28 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.25.80/28 [90/10368] via 10.55.43.45, 12:18:24, Port-channel18
D        10.55.26.64/26 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.26.192/26 [90/10368] via 10.55.43.45, 7w0d, Port-channel18
D        10.55.32.0/24 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.33.0/24 [90/10368] via 10.55.43.33, 7w0d, Port-channel19
D        10.55.34.0/24 [90/10368] via 10.55.43.58, 7w0d, Port-channel20
D        10.55.38.0/26 [90/10368] via 10.55.43.58, 00:55:14, Port-channel20

[chrihussey]

Oops. Sorry I missed this while typing up my earlier response. So if ISP 1 fails, is the route withdrawn immediately and the route to ISP 2 remains or do both go away?

Also, could it be that your end is converging quick enough and that the delay is in the other side of the MPLS cloud knowing that it is inaccessible via ISP 1?

[Daniel Freitas]

 Both go away.

Could be, but that doesn't explain why both default routes always have the same uptime, like this:

D*EX  0.0.0.0/0 [170/15360] via 10.55.43.41, 1d21h, TenGigabitEthernet2/1/1
                [170/15360] via 10.55.43.37, 1d21h, TenGigabitEthernet1/1/1

They got a flap everytime one ISP goes down and flap again when the ISP is back.

[Julio E. Moisa]

Are you sure that both ISP are not using the same path to internet? Is the providers advertising the default route? You could redistribute the static default route to the Core manually with different metrics. 

[Daniel Freitas]

I'm originating this default route on my internet exit, on the data center and from there propagating the route to both MPLS providers. Since I manage my own CEs, I'm pretty sure that the providers are not influencing the process at all.

[chrihussey]

Need clarification regarding the default route. The configs supplied only show redistribution of BGP into EIGRP with a route map. The assumption was that that was how the default route got into EIGRP.

Can you explain what you mean by saying that you originate the default route on the internet exit? Is it a BGP route from the MPLS provider, a static route, etc?

Thanks