To finish up with IS-IS for now, I’m going to go through the set up of a four router, three area IS-IS network that uses a hub and spoke frame relay network. Here is a drawing of the network:
The goal is to simply have all the addresses, including the loopbacks, appear in the routing tables of all routers.
R0 is pretty easy to set up, it is a level 1 router in area 49.0001
interface Loopback0 ip address 192.168.0.1 255.255.255.0 ip router isis interface Ethernet0 ip address 10.50.0.1 255.255.255.0 ip router isis isis circuit-type level-1 router isis net 49.0001.0100.5000.0001.00
Moving on to R3, set up the basics. Note that since I’m using a multipoint frame relay setup, I have to set up frame-relay maps for clns (IP is using inverse arp)
interface Loopback0 ip address 192.168.3.1 255.255.255.0 ip router isis ! interface Ethernet0 ip address 10.50.0.2 255.255.255.0 ip router isis ! interface Serial0 no ip address encapsulation frame-relay no fair-queue ! interface Serial0.1 multipoint ip address 10.51.0.3 255.255.255.248 ip router isis frame-relay map clns 121 broadcast frame-relay map clns 120 broadcast frame-relay interface-dlci 120 frame-relay interface-dlci 121 router isis net 49.0001.0100.5000.0002.00
At this point, I’d expect R0 and R3 to be exchanging routes:
r3#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
r0 Et0 0060.5cf3.bb1e Up 25 L1 IS-IS
r3#show ip route
…
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.50.0.0/24 is directly connected, Ethernet0
C 10.51.0.0/29 is directly connected, Serial0.1
i L1 192.168.0.0/24 [115/20] via 10.50.0.1, Ethernet0
C 192.168.3.0/24 is directly connected, Loopback0
Excellent. On to R1
interface Loopback0 ip address 192.168.1.1 255.255.255.0 ip router isis ! interface Ethernet0 no ip address shutdown ! interface Serial0 no ip address encapsulation frame-relay ! interface Serial0.102 point-to-point ip address 10.51.0.1 255.255.255.248 ip router isis frame-relay interface-dlci 102 isis circuit-type level-2-only ! router isis net 49.0002.1921.6800.1001.00
Nothing. Checking “clns neighbors” on R1 shows nothing, on R3 I see
1921.6800.1001 Se0.1 DLCI 120 Up 256 IS ES-IS
Logs on R1 show:
3d03h: ISIS-Adj: Rec L2 IIH from DLCI 102 (Serial0.102), cir type L1L2, cir id0 3d03h: ISIS-Adj: Multi-point IIH received on point-to-point interface: ignoredH
I found IS-IS Network Types and Frame Relay Interfaces on Cisco’s site, it looks like the interface types must match.
r1:
no interface Serial0.102 point-to-point interface Serial0.2 mult ip address 10.51.0.1 255.255.255.248 ip router isis frame-relay interface-dlci 102 isis circuit-type level-2-only
(Note how I had to change the subinterface number, otherwise IOS won’t let me change the interface type)
r1#show clns neighbors System Id Interface SNPA State Holdtime Type Protocol 0100.5000.0002 Se0.2 DLCI 102 Init 9 L2 IS-IS
Damn. I forgot to map clns broadcasts on R1:
interface Serial0.2 mult frame-relay map clns 102 broadcast r1#show clns neighbors System Id Interface SNPA State Holdtime Type Protocol r3 Se0.2 DLCI 102 Up 27 L2 IS-IS
Some testing:
r1#show clns neighbors
System Id Interface SNPA State Holdtime Type Protocol
r3 Se0.2 DLCI 102 Up 27 L2 IS-IS
r1#show ip route
...
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
i L2 10.50.0.0/24 [115/20] via 10.51.0.3, Serial0.2
C 10.51.0.0/29 is directly connected, Serial0.2
i L2 192.168.0.0/24 [115/30] via 10.51.0.3, Serial0.2
C 192.168.1.0/24 is directly connected, Loopback0
i L2 192.168.3.0/24 [115/20] via 10.51.0.3, Serial0.2
r1#ping 192.168.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 48/52/60 ms
On R1, since it is in a different area than R0 and R3, all their routes show up as L2.
R2 is basically a duplicate of R1, so I won’t go into it here (not to mention the load on it doesn’t support IS-IS)
One thing, though, is I’d like to have R3 originate a default route:
r3:
ip route 0.0.0.0 0.0.0.0 10.50.0.253 router isis default-information originate
It looks like only L2 routers can originate a default route, since all L1 routers should be going to an L2 router anyway. More information to follow in an update…
Updated
Yes, an L2 router connected to multiple areas sets the ATT bit in the LSP, which instructs the L1 routers to use it as a default route. This can be seen from R0’s routing table after R3 was set up in area 49.0002:
r0>show ip route ... Gateway of last resort is 10.50.0.2 to network 0.0.0.0 ... i*L1 0.0.0.0/0 [115/10] via 10.50.0.2, Ethernet0
Cisco’s IS-IS Overview, under example 5:
A Level 1/Level 2 router that is attached to another area will set the “attached bit” in its Level 1 LSP; all the Level 1 ISs in an area will get a copy of this LSP and know where to forward packets to destinations outside the area. If the routers are running Integrated IS-IS, a default IP route will automatically be installed in the Level 1 routers pointing toward the nearest Level 1/Level 2 router that originally set the attached bit in its Level 1 LSP. A Level 1/Level 2 router that is not attached to another area can also detect that a Level 2-only neighbor is attached to another area and set the “attached bit” on behalf of this Level 2-only neighbor.
If there is more than one point to exit the area (multiple Level 2-capable routers), the closest Level 1/Level 2 router is selected based on the cost. If there are two equal cost paths then the traffic may load balance over the two paths.
No user commented in " IS-IS, multiareas and frame-relay "
Follow-up comment rss or Leave a TrackbackLeave A Reply