Routing Protocols

Tutorial: OSPF Network Types and Frame Relay Part 2

Thanks for visiting! If you're new here, you may want to subscribe to my RSS feed. This blog posts regular tutorials, news, and study tips about networking, especially about Cisco CCIE related topics. Go ahead, subscribe to the rss feed! You can also receive updates from this blog via email. Thanks for visiting!

In our last article we looked at the Broadcast and Non-Broadcast OSPF network types. We will be continuing our OSPF Network Type series of articles by looking at Point-to-Multipoint and Point-to-Multipoint Non-Broadcast network types.

Once again, we will be using the following topology for this tutorial:

Dynagen Configuration

ghostios = True
sparsemem = True
model = 3640

[localhost]

    [[3640]]
        image = \Program Files\Dynamips\images\c3640-jk9o3s-mz.124-12.bin
        # On Linux / Unix use forward slashes:
        # image = /opt/7200-images/c7200-jk9o3s-mz.124-7a.image
        ram = 96

    [[ROUTER R1]]
        f0/0 = LAN 1
        s1/0 = FRAME 1
        console = 2000
        model = 3640

    [[ROUTER R2]]
        f0/0 = LAN 2
        s1/0 = FRAME 2
        console = 2001
        model = 3640

    [[ROUTER R3]]
        f0/0 = LAN 3
        s1/0 = FRAME 3
        console = 2002
        model = 3640

    [[FRSW FRAME]]
        1:102 = 2:201
        1:103 = 3:301

You can download the .net file for dynagen/dynamips here.

OSPF Over Frame Relay – Point-to-Multipoint Network Type

OSPF treats Point-to-Multipoint networks as a collection of point-to-point links. A DR/BDR is not required in these networks as OSPF Packets are unicast to known neighbors. Lets have a look at the configuration:

R1

hostname R1
!
interface fastEthernet0/0
 ip address 1.1.1.1 255.255.255.0
!
interface Serial1/0
 ip address 192.168.1.1 255.255.255.0
 encapsulation frame-relay
 frame-relay map ip 192.168.1.2 102 broadcast
 frame-relay map ip 192.168.1.3 103 broadcast
 no frame-relay inverse-arp
 ip ospf network point-to-multipoint
!
router ospf 1
 router-id 1.1.1.1
 network 0.0.0.0 255.255.255.255 area 0

R2

hostname R2
!
interface fastEthernet0/0
 ip address 2.2.2.2 255.255.255.0
!
interface Serial1/0
 ip address 192.168.1.2 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 192.168.1.1 201 broadcast
 frame-relay map ip 192.168.1.3 201
 no frame-relay inverse-arp
 ip ospf network point-to-multipoint
!
router ospf 1
 router-id 2.2.2.2
 network 0.0.0.0 255.255.255.255 area 0

R3

hostname R3
!
interface fastEthernet0/0
 ip address 3.3.3.3 255.255.255.0
!
interface Serial1/0
 ip address 192.168.1.3 255.255.255.0
 encapsulation frame-relay
 frame-relay map ip 192.168.1.1 301 broadcast
 frame-relay map ip 192.168.1.2 301
 no frame-relay inverse-arp
 ip ospf network point-to-multipoint
!
router ospf 1
 router-id 3.3.3.3
 network 0.0.0.0 255.255.255.255 area 0

You can see the configuration above is fairly straight forward. We don’t need to worry about a DR as Point-to-Multipoint networks don’t require one. Let’s verify the configuration:

R1#
*Mar  1 00:03: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial1/0 from LOADING to FULL, Loading Done
*Mar  1 00:03: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial1/0 from LOADING to FULL, Loading Done
R1#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/  -        00:01:39    192.168.1.2     Serial1/0
3.3.3.3           0   FULL/  -        00:01:39    192.168.1.3     Serial1/0

You can see the output of the show ip ospf neighbors command above. We have full adjacency with R2 and R3. You can also see that there is no DR/BDR relationship between any of the routers.

Lets verify the network types and timers:

Serial1/0 is up, line protocol is up
  Internet Address 192.168.1.3/24, Area 0
  Process ID 1, Router ID 3.3.3.3, Network Type POINT_TO_MULTIPOINT, Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT,
  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:03
  Supports Link-local Signaling (LLS)
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 1.1.1.1
  Suppress hello for 0 neighbor(s)
FastEthernet0/0 is up, line protocol is up
  Internet Address 3.3.3.3/24, Area 0
  Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 3.3.3.3, Interface address 3.3.3.3
  No backup designated router on this network
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:04
  Supports Link-local Signaling (LLS)
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 0, maximum is 0
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 0, Adjacent neighbor count is 0
  Suppress hello for 0 neighbor(s)

You can see above the default timers on a Point-to-Multipoint network is 30 seconds and 120 seconds for the hello and dead intervals respectively. So far this looks not very different from the other network types other than the ip ospf network type command. Lets take a look more closely at R3 and R3’s routing table:

R3#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           0   FULL/  -        00:01:42    192.168.1.1     Serial1/0

Looks like R3 has only formed a neighbor relationship with R1. Wait a minute, if R3 only forms a neighbor relationship with R1 and there is no DR relationship, does that mean that R3 has no idea about the networks from R2? The answer to this question lies in the route table of R3. Let’s compare this to the route table when we used the Broadcast network type:

Route Table Using Point-to-Multipoint Network Type

R3#sh ip route
Codes: 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
O       1.1.1.0 [110/65] via 192.168.1.1, 00:10:26, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O       2.2.2.0 [110/129] via 192.168.1.1, 00:10:26, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, FastEthernet0/0
     192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
O       192.168.1.1/32 [110/64] via 192.168.1.1, 00:10:26, Serial1/0
C       192.168.1.0/24 is directly connected, Serial1/0
O       192.168.1.2/32 [110/128] via 192.168.1.1, 00:10:26, Serial1/0

Route Table Using Broadcast Network Type

R3#sh ip route
Codes: 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
O       1.1.1.0 [110/65] via 192.168.1.1, 00:09:29, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O       2.2.2.0 [110/65] via 192.168.1.2, 00:09:29, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, Serial1/0

If we compare the route tables, we see that the route table for Point-to-Multipoint has three differences:

O       2.2.2.0 [110/129] via 192.168.1.1, 00:10:26, Serial1/0
O       192.168.1.1/32 [110/64] via 192.168.1.1, 00:10:26, Serial1/0
O       192.168.1.2/32 [110/128] via 192.168.1.1, 00:10:26, Serial1/0

The route to 2.2.2.0 network is via 192.168.1.1 instead of 192.168.1.2. We also have two /32 routes for the endpoints in the frame-relay cloud.

The Point-to-Multipoint network type treats the NBMA network as a series of point-to-point links. OSPF treats it as if we are squeezing a single subnet over two point to point links. In this case all of R3’s routes are via R1. The layer 3 topology is mirroring the layer 2 topology.

Because Point-to-Multipoint treats the NBMA network as a series of point-to-point links, we could even get rid of the frame relay map between R3 and R2 and the routes should still be fine! Lets try it:

R3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#int s1/0
R3(config-if)#no frame-relay map ip 192.168.1.2 301
R3(config-if)#end
*Mar  1 01:59:25.239: %SYS-5-CONFIG_I: Configured from console by console
R3#sh run int s1/0
Building configuration...

Current configuration : 227 bytes
!
interface Serial1/0
 ip address 192.168.1.3 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-multipoint
 serial restart-delay 0
 frame-relay map ip 192.168.1.1 301 broadcast
 no frame-relay inverse-arp
end

The configuration above shows we no longer have a mapping to R2. Let’s have a look at the effect this has. We’ll clear the OSPF processes and take a look at reachability afterwards:

R3#clear ip ospf pro
Reset ALL OSPF processes? [no]: yes
R3#
*Mar  1 01:59: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial1/0 from FULL to DOWN,
Neighbor Down: Interface down or detached
*Mar  1 01:59: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial1/0 from LOADING to FULL, Loading Done

R3#sh ip route
Codes: 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
O       1.1.1.0 [110/65] via 192.168.1.1, 00:00:00, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O       2.2.2.0 [110/129] via 192.168.1.1, 00:00:00, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, FastEthernet0/0
     192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
O       192.168.1.1/32 [110/64] via 192.168.1.1, 00:00:00, Serial1/0
C       192.168.1.0/24 is directly connected, Serial1/0
O       192.168.1.2/32 [110/128] via 192.168.1.1, 00:00:00, Serial1/0
R3#ping 2.2.2.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 96/229/428 ms

This still works because the OSPF point-to-multipoint network introduced an extra hop between R3 and the ethernet network on R2. Instead of going straight to R2’s 192.168.1.2 address to get to that segment we go via R1’s 192.168.1.1. OSPF has inserted an extra hop via R1 to mirror that of the layer 2 topology! Cool huh?

OSPF Over Frame Relay – Point-to-Multipoint Non-Broadcast Network Type

The point-to-multipoint non-broadcast network type is basically the same as the point-to-multipoint network type except it is useful in scenarios where we have no broadcast capabilities. Lets reconfigure our layer 2 topology and take away the pseudo broadcast capability of frame relay:

R1

hostname R1
!
interface fastEthernet0/0
 ip address 1.1.1.1 255.255.255.0
!
interface Serial1/0
 ip address 192.168.1.1 255.255.255.0
 encapsulation frame-relay
 frame-relay map ip 192.168.1.2 102
 frame-relay map ip 192.168.1.3 103
 no frame-relay inverse-arp
 ip ospf network point-to-multipoint non-broadcast
!
router ospf 1
 router-id 1.1.1.1
 network 0.0.0.0 255.255.255.255 area 0
 neighbor 192.168.1.2
 neighbor 192.168.1.3

R2

hostname R2
!
interface fastEthernet0/0
 ip address 2.2.2.2 255.255.255.0
!
interface Serial1/0
 ip address 192.168.1.2 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 192.168.1.1 201
 frame-relay map ip 192.168.1.3 201
 no frame-relay inverse-arp
 ip ospf network point-to-multipoint non-broadcast
!
router ospf 1
 router-id 2.2.2.2
 network 0.0.0.0 255.255.255.255 area 0

R3

hostname R3
!
interface fastEthernet0/0
 ip address 3.3.3.3 255.255.255.0
!
interface Serial1/0
 ip address 192.168.1.3 255.255.255.0
 encapsulation frame-relay
 frame-relay map ip 192.168.1.1 301
 frame-relay map ip 192.168.1.2 301
 no frame-relay inverse-arp
 ip ospf network point-to-multipoint non-broadcast
!
router ospf 1
 router-id 3.3.3.3
 network 0.0.0.0 255.255.255.255 area 0

You will notice with the configuration above we have once again removed the broadcast statement from the frame-relay map statements so no broadcasts will be propogated across that network. R1 has R2 and R3 defined as its neighbors and will unicast updates to them. Lets verify the configuration:

R1#
*Mar  1 02:43: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial1/0 from LOADING to FULL, Loading Done
*Mar  1 02:43: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial1/0 from LOADING to FULL, Loading Done
R1#sh ip ospf nei

Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/  -        00:01:31    192.168.1.2     Serial1/0
3.3.3.3           0   FULL/  -        00:01:31    192.168.1.3     Serial1/0

Once again you can see that R1 has established adjacencies with R2 and R3. No DR/BDR relationship is established in a point-to-multipoint non-broadcast network. Lets verify the network type and timers:

R1#sh ip ospf int
Serial1/0 is up, line protocol is up
  Internet Address 192.168.1.1/24, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT,
  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:23
  Supports Link-local Signaling (LLS)
  Index 2/2, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 2, Adjacent neighbor count is 2
    Adjacent with neighbor 2.2.2.2
    Adjacent with neighbor 3.3.3.3
  Suppress hello for 0 neighbor(s)
FastEthernet0/0 is up, line protocol is up
  Internet Address 1.1.1.1/24, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State DR, Priority 1
  Designated Router (ID) 1.1.1.1, Interface address 1.1.1.1
  No backup designated router on this network
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:01
  Supports Link-local Signaling (LLS)
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 0, maximum is 0
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 0, Adjacent neighbor count is 0
  Suppress hello for 0 neighbor(s)

You can see the default timers for a point-to-multipoint non-broadcast network are 30 seconds and 120 seconds for the hello and dead intervals respectively.

R3#sh ip route
Codes: 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
O       1.1.1.0 [110/65] via 192.168.1.1, 00:20:04, Serial1/0
     2.0.0.0/24 is subnetted, 1 subnets
O       2.2.2.0 [110/129] via 192.168.1.1, 00:20:04, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
C       3.3.3.0 is directly connected, FastEthernet0/0
     192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
O       192.168.1.1/32 [110/64] via 192.168.1.1, 00:20:04, Serial1/0
C       192.168.1.0/24 is directly connected, Serial1/0
O       192.168.1.2/32 [110/128] via 192.168.1.1, 00:20:05, Serial1/0

Looking at the routing table on R3, we can again see that the layer 3 routing mirror’s the layer 2 switching, with everything going through R1.

The other thing that differentiates point-to-multipoint from point-to-multipoint non-broadcast is the ability to define the costs of
routes originating from a particular neighbor.

For example:

router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 network 0.0.0.0 255.255.255.255 area 0
 neighbor 192.168.1.2 cost 100
 neighbor 192.168.1.3

Here we have defined all updates coming from R2 to have a cost of 100. Lets have a look at the routing table before and after this change:

Before:

R1(config-router)#do sh ip route
Codes: 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, FastEthernet0/0
     2.0.0.0/24 is subnetted, 1 subnets
O       2.2.2.0 [110/65] via 192.168.1.2, 00:24:07, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 192.168.1.3, 00:24:07, Serial1/0
     192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
C       192.168.1.0/24 is directly connected, Serial1/0
O       192.168.1.3/32 [110/64] via 192.168.1.3, 00:24:07, Serial1/0
O       192.168.1.2/32 [110/64] via 192.168.1.2, 00:24:07, Serial1/0

After:

R1(config-router)#do sh ip route
Codes: 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, FastEthernet0/0
     2.0.0.0/24 is subnetted, 1 subnets
O       2.2.2.0 [110/101] via 192.168.1.2, 00:00:02, Serial1/0
     3.0.0.0/24 is subnetted, 1 subnets
O       3.3.3.0 [110/65] via 192.168.1.3, 00:00:02, Serial1/0
     192.168.1.0/24 is variably subnetted, 3 subnets, 2 masks
C       192.168.1.0/24 is directly connected, Serial1/0
O       192.168.1.3/32 [110/64] via 192.168.1.3, 00:00:02, Serial1/0
O       192.168.1.2/32 [110/100] via 192.168.1.2, 00:00:02, Serial1/0

You can see the route cost to the networks that R2 updated were increased to 100 (directly connected 192.168.1.2), and 101 (2.2.2.0/24). This could be useful is you have a network being advertised by both R2 and R3 and you would prefer one route over the other.

In the next article we will be looking at the Point-to-Point and Loopback network types.

HTH. Now back to labs!

Summary:

• OSPF treats Point-to-Multipoint networks as a series of point-to-point links, mirroring the layer 2 topology.
• Point-to-Multipoint networks don’t have DR/BDR relationships.
• Point-to-Multipoint networks advertise /32 routes for all the frame-realy endpoints.
• Point-to-Multipoint networks have Hello and Dead intervals of 30 seconds and 120 seconds respectively.
• Point-to-Multipoint non-broadcast networks are very similar to point-to-multipoint networks except that they work over layer 2 topologies that have no broadcast capability
• Point-to-Multipoint non-broadcast networks allow you to define cost on a per neighbor basis.

Resources:

• Dynamips/Dynagen .net configuration file

© 2008 Arden Packeer. All rights reserved. The opinions expressed herein are my own personal opinions and do not represent my employer's view in anyway. This material is not sponsored or endorsed by Cisco Systems, Inc. Cisco, Cisco Systems, CCIE and the CCIE Logo are trademarks of Cisco Systems, Inc. and its affiliates