EIGRP is giving me a headache...

Drakonblayde

Alright, I'm taking BSCI in about a week and a half, and I'm running through labs. I have one lab which has an AS with one router connected to another outside the AS. The router outside the AS has no routing protocol on it, just an interface into one of the AS routers and a loopback that's supposed to represent the outside world.

Part of the parameters of the lab is to propagate a persisten default route through EIGRP to the rest of the AS and let them be able to ping that router.

Now, I used the ip default-network command. The network is known to EIGRP, advertised via the network command. The downstream routers properly install it as the gateway of last resort. The problem I'm running into is that the router I issued the ip default-nework command on is not setting the gateway of last resort. The route *is* flagged as a candidate default route in the routing table, but I can't ping the loopback of the outside router. I can ping the interface that's directly connected to the inside router.

Now, here's the fun part. If I install a normal quad-zero default route out that interface, I *can* ping the loopback. But none of my downstream routers can. As soon as it hits the router connected to the outside, the traffic dies. Just for the hell of it, wiped the config, started over, and instead of using ip default-network, I just added a static quad zero and redistributed it into EIGRP. Worked like a charm. However, the lab doesn't want me to redistribute, it wants it propagted through EIGRP.

So my major problem is that the router I issued the ip default-gateway command on is not setting the gateway of last resort, my other routers are, the route is flagged as a candidate default route, and it's not working. And I have no idea why and it's irritating the living hell out of me!

Help please

tunerX

Is the default network a directly connected network? Or is it reachable via a second router?

If the router is not directly connected to the default network then you have to install a static route to the default network.

If it is a connected network then the default network statement will automatically allow EIGRP to inject a default-route in its routing table.

Post configs and a diagram, otherwise we can only guess what you are trying to accomplish.

Drakonblayde

Yeah, the router is directly connected. It's all running in my lab at work, I'll post my show run, diagrams and routing tables when I get in Monday morning. I know it's going to be something simple that I overlooked, but I'm pretty sure I did it all right which is why this is messing with me.

Yankee

Is the default network participating in eigrp (network x.x.x.x)? Can't tell from your question but seems like it may not be playing in eigrp.

Yankee

Drakonblayde

ISP (Not in the AS)
|
R1 (AS 100)
| | (Both AS 100)
R2 R3

ISP - No routing protocol, Fa0/0 172.16.0.1/24, Lo0 200.20.20.1/32 (loopback simulating rest of world)
R1 - Fa0/0, connected to Fa0/0 on ISP, 172.16.0.2/24
S0/0 connected to R2, 192.168.50.1/30
S0/1 connected to R3, 192.168.50.5/30
Running EIGRP, AS 100
R2 - S0/0 connected to R1, 192.168.50.2/30
Fa0/0 192.168.100.1/24
lo0 10.10.64.1/24
lo1 10.10.80.1/24
lo2 10.10.96.1/24
lo3 10.10.112.1/24
Running EIGRP, AS 100
R3 - S0/0 connected to R1, 192.168.50.6/30
Fa0/0 192.168.200.1/24
lo0 10.10.240.1/24
lo1 10.10.244.1/24
lo2 10.10.10.248/24
lo3 10.10.10.252.1/24
Running EIGRP, AS 100


Routing Tables:

ISP:
Gateway of last resort is not set

200.20.20.0/32 is subnetted, 1 subnets
C 200.20.20.1 is directly connected, Loopback0
172.16.0.0/24 is subnetted, 1 subnets
C 172.16.0.0 is directly connected, Ethernet0/0

R1:

Gateway of last resort is not set

* 172.16.0.0/24 is subnetted, 1 subnets
C* 172.16.0.0 is directly connected, Ethernet0/0
D 192.168.200.0/24 [90/2172416] via 192.168.50.6, 00:02:47, Serial0/1
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.10.64.0/18 [90/2297856] via 192.168.50.2, 00:05:37, Serial0/0
D 10.10.240.0/20 [90/2297856] via 192.168.50.6, 00:02:47, Serial0/1
192.168.50.0/30 is subnetted, 2 subnets
C 192.168.50.0 is directly connected, Serial0/0
C 192.168.50.4 is directly connected, Serial0/1

R2:
Gateway of last resort is 192.168.50.1 to network 172.16.0.0

172.16.0.0/24 is subnetted, 1 subnets
D* 172.16.0.0 [90/2195456] via 192.168.50.1, 00:00:54, Serial0
D 192.168.200.0/24 [90/2684416] via 192.168.50.1, 00:03:38, Serial0
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
D 10.10.64.0/18 is a summary, 00:06:35, Null0
C 10.10.64.0/24 is directly connected, Loopback0
C 10.10.80.0/24 is directly connected, Loopback1
C 10.10.96.0/24 is directly connected, Loopback2
C 10.10.112.0/24 is directly connected, Loopback3
D 10.10.240.0/20 [90/2809856] via 192.168.50.1, 00:03:40, Serial0
192.168.50.0/30 is subnetted, 2 subnets
C 192.168.50.0 is directly connected, Serial0
D 192.168.50.4 [90/2681856] via 192.168.50.1, 00:05:12, Serial0

R3:
Gateway of last resort is 192.168.50.5 to network 172.16.0.0

172.16.0.0/24 is subnetted, 1 subnets
D* 172.16.0.0 [90/2195456] via 192.168.50.5, 00:01:18, Serial0
C 192.168.200.0/24 is directly connected, FastEthernet0
10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks
D 10.10.64.0/18 [90/2809856] via 192.168.50.5, 00:04:05, Serial0
D 10.10.240.0/20 is a summary, 00:04:08, Null0
C 10.10.240.0/24 is directly connected, Loopback0
C 10.10.244.0/24 is directly connected, Loopback1
C 10.10.248.0/24 is directly connected, Loopback2
C 10.10.252.0/24 is directly connected, Loopback3
192.168.50.0/30 is subnetted, 2 subnets
D 192.168.50.0 [90/2681856] via 192.168.50.5, 00:04:06, Serial0
C 192.168.50.4 is directly connected, Serial0

Configurations:

ISP:
Current configuration : 449 bytes
version 12.3
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname ISP
boot-start-marker
boot-end-marker
no aaa new-model
ip subnet-zero
ip cef
!nterface Loopback0
ip address 200.20.20.1 255.255.255.255
interface Ethernet0/0
ip address 172.16.0.1 255.255.255.0
half-duplex
no ip http server
ip classless
line con 0
line aux 0
line vty 0 4
end

R1:
urrent configuration : 594 bytes
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
hostname R1
ip subnet-zero
interface Ethernet0/0
ip address 172.16.0.2 255.255.255.0
half-duplex
interface Serial0/0
ip address 192.168.50.1 255.255.255.252
clockrate 64000
interface Serial0/1
ip address 192.168.50.5 255.255.255.252
router eigrp 100
network 172.16.0.0 0.0.0.255
network 172.16.0.0
network 192.168.50.0
no auto-summary
ip classless
ip default-network 172.16.0.0
ip http server
line con 0
line aux 0
line vty 0 4
login
end

R2:
urrent configuration : 805 bytes
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
hostname R2
memory-size iomem 15
ip subnet-zero
interface Loopback0
ip address 10.10.64.1 255.255.255.0
interface Loopback1
ip address 10.10.80.1 255.255.255.0
interface Loopback2
ip address 10.10.96.1 255.255.255.0
interface Loopback3
ip address 10.10.112.1 255.255.255.0
interface FastEthernet0
ip address 192.168.100.1 255.255.255.0
speed auto
interface Serial0
ip address 192.168.50.2 255.255.255.252
ip summary-address eigrp 100 10.10.64.0 255.255.192.0 5
no fair-queue
router eigrp 100
network 10.0.0.0
network 192.168.50.0
network 192.168.100.0
no auto-summary
ip classless
no ip http server
line con 0
line aux 0
line vty 0 4
login
end

R3:
urrent configuration : 878 bytes
version 12.2
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname R3
memory-size iomem 25
ip subnet-zero
interface Loopback0
ip address 10.10.240.1 255.255.255.0
interface Loopback1
ip address 10.10.244.1 255.255.255.0
interface Loopback2
ip address 10.10.248.1 255.255.255.0
interface Loopback3
ip address 10.10.252.1 255.255.255.0
interface FastEthernet0
ip address 192.168.200.1 255.255.255.0
speed auto
interface Serial0
ip address 192.168.50.6 255.255.255.252
ip summary-address eigrp 100 10.10.240.0 255.255.240.0 5
no fair-queue
clockrate 64000
router eigrp 100
network 10.0.0.0
network 192.168.50.0
network 192.168.200.0
no auto-summary
no eigrp log-neighbor-changes
ip classless
no ip http server
line con 0
line aux 0
line vty 0 4
login
end

Drakonblayde

As you can see, the default network (172.16.0.0) is participating in EIGRP, and it's being passed to the downstream routers as an EIGRP route and a default route.

Drakonblayde

Ok, I'm confused now. I came in this morning and redid all the configs. This time, when I added the default quad zero route to R1, It's routing table changed to this:

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

* 172.16.0.0/24 is subnetted, 1 subnets
C* 172.16.0.0 is directly connected, Ethernet0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.10.64.0/18 [90/2297856] via 192.168.50.2, 00:24:59, Serial0/0
D 10.10.240.0/20 [90/2297856] via 192.168.50.6, 00:22:09, Serial0/1
192.168.50.0/30 is subnetted, 2 subnets
C 192.168.50.0 is directly connected, Serial0/0
C 192.168.50.4 is directly connected, Serial0/1
S* 0.0.0.0/0 is directly connected, Ethernet0/0

And *now* everything can ping the loopback on the ISP router.

If I pull it back out, it goes back to what I've got shown above and no one can ping the ISP loopback.

But even with that.. it seems sorta backwards to me. Is it supposed to work like that (ie, have to have a manually defined default route out of the AS border router) or should the router on which the ip default-network command obey it's own instructions on where to send last resort traffic?

Yankee

Your ISP has no idea how to return to AS100. Add a default route back to AS100 and things will be reach able.

Yankee

Drakonblayde

Alright, just for kicks, I did that. Now the ISP router can ping everything in the EIGRP AS, but nothing can ping the ISP router without the manually inserted default route on R1.

That also doesn't really make sense. If it was as simple as the ISP not knowing how to get to AS100, then why would adding a default route to R1 instead of the ISP router make things all of a sudden work? R1 would know how to get outside, but the ISP still wouldn't know what to do with the return traffic.

Now keep in mind, when I was trying to ping the ISP loopback from R1, I did use an extended ping and specified the source address as the 172.16.0.0 network one (part of the lab was also to have R1 NAT traffic from the downstream, so I wasn't concerend with R2 and R3 being able to ping the ISP before I implemented NAT, but when R1 can't ping ISP, there's a problem that needs resolving). If R1 was obeying the ip default-network command, it should have forwarded that traffic out the ethernet interface. ISP sees a packet incoming for 200.20.20.1 from 172.16.0.2. 200.20.20.0 is in it's routing table since it's directly connected. It hits the loopback, the return traffic is to a node on the 172.16.0.0 network, which is another directly connected network, so it does know how to get to it.

If I add the ISP to the AS, everything works fine. If I redistribute the default route into EIGRP, everything works fine. So I'm reasonably sure it's not bad equipment (I've had 3 different routers functioning as R1, and I've swapped out my WIC cards for newer ones just in case). As near as I can pinpoint, the problem is simply that R1 will not install a gateway of last resort with the ip default-network command. Now the letter of the lab says to advertise a persistent default route through EIGRP from R1, and it is doing that, my downstream routers are just happy and peachy. And with the quad zero installed, everything works the way it should. I was just under the impression that the ip default-network command was supposed to take effect on the router on which it was issued.

tunerX

It will only install a gateway of last resort if the network is not directly connected.

Based on your configs you are doing it the right way.

For a directly connected network

---

You use ip default-network to flag a candidate route. Eigrp then, automatically, distributes that route to all neighbors. If the network is in a neighbors routing table then it will be added as a gateway of last resort and will also be flagged as a candidate default route. To have R1 use a gateway of last resort you must use the 0.0.0.0 network.

For a network that is not in the routing table

---

The other way to do it is to have the network one hop away. Make a network in the ISP cloud that will be the default. You then add that the default-network and add a static route to that network. You then need to redistribute that route into EIGRP. After this EIGRP will propagate the default network and set a gateway of last resort.

Drakonblayde

tunerX wrote:

It will only install a gateway of last resort if the network is not directly connected.
For a directly connected network

---

You use ip default-network to flag a candidate route. Eigrp then, automatically, distributes that route to all neighbors. If the network is in a neighbors routing table then it will be added as a gateway of last resort and will also be flagged as a candidate default route. To have R1 use a gateway of last resort you must use the 0.0.0.0 network.

Ah, thank you. That's what I needed to know. I haven't run across any documentation that mentioned that. I've run across alot of text that stated IGRP and EIGRP don't know how to deal with a quad 0 network, but EIGRP apparently does, because everything worked fine when I redistributed a quad 0 route into it. So apparently there's a bit of confusion with EIGRP. At any rate, I'm back to boning up on BGP, glad I finally got a definitive answer on that bloody issue, hehe. Thanks man

Yankee

Sorry for being incomplete in my answer. I had seen Turner had already explained the default network and meant to be just adding to it with my quick statement about the ISP not knowing how to get back. Limited time and early morning answers often lead me to brief answers....sorry.

Yankee

PS. BGP is 100 times more complicated than EIGRP, so good luck and have fun with it

Drakonblayde

Yankee wrote:

PS. BGP is 100 times more complicated than EIGRP, so good luck and have fun with it

Yeah, I didn't find EIGRP all that hard, just that one thing was messing with me. BGP is a bloody bear though. Finishing up my OSPF labs today, unfortunately our routers don't have Enterprise loaded on them so I can't do IS-IS, gonna have to rely on a sim for that configuration exercise, and then my full time until the exam is devoted to BGP. Hopefully I'll get lucky and won't get that wide a selection of questions on BGP, but I know my luck....

KMAN24

What labs are you following ? Trying to decide on which way to go before the purchase. Seems like a forever wait for the Boson CCNP.

Ken

Drakonblayde

Cisco Academy Curriculum, mainly. I'm not an Academy student anymore, but since I was the one that setup my Academy's internal web server, I sorta had access to it hehe

It's an interesting experience, since I have no way of knowing whether or not my answers are right except for by achieving the results of the lab. It's a hell of a learning experience