Repairing OSPF AREA 0 - Bandages For OSPF

Today I would like to talk about some crazy stuff. It's about repairing OSPF AREA 0. Repairing...?

Yes, it's very interesting scenario indeed which I learned long back while preparing for R&S written exam. Here it is:

The task requirement was something like this:

R1's S0/0, R2's S0/0, R4 , R5 are configured in OSPF AREA 0.
R1's S0/1, R2's S0/1 and R3 are configured in OSPF AREA 1.


R4 should be able to reach R5 even if Frame-Relay Link between R1 & R2 goes down.


Now lets start with basic configuration and see what kind of issues appears and how to fix those.


*****************
* CONFIGURATION *
*****************
R1(config)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
FastEthernet0/0 is up, line protocol is up
  Internet address is 14.14.14.1/24
Serial0/0 is up, line protocol is up
  Internet address is 12.12.12.1/24
Serial0/1 is up, line protocol is up
  Internet address is 13.13.13.1/24

R1(config)#do sh run | s r o
router ospf 100
 router-id 11.11.11.11
 log-adjacency-changes
 network 12.12.12.1 0.0.0.0 area 0
 network 13.13.13.1 0.0.0.0 area 1
 network 14.14.14.1 0.0.0.0 area 0

R2(config)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
FastEthernet0/0 is up, line protocol is up
  Internet address is 25.25.25.2/24
Serial0/0 is up, line protocol is up
  Internet address is 12.12.12.2/24
Serial0/1 is up, line protocol is up
  Internet address is 23.23.23.2/24

R2(config)#do sh run | s r o
router ospf 200
 router-id 22.22.22.22
 log-adjacency-changes
 network 12.12.12.2 0.0.0.0 area 0
 network 23.23.23.2 0.0.0.0 area 1
 network 25.25.25.2 0.0.0.0 area 0

R3(config)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
Serial0/0 is up, line protocol is up
  Internet address is 23.23.23.3/24
Serial0/1 is up, line protocol is up
  Internet address is 13.13.13.3/24

R3(config)#do sh run | s r o
router ospf 300
 router-id 33.33.33.33
 log-adjacency-changes
 network 13.13.13.3 0.0.0.0 area 1
 network 23.23.23.3 0.0.0.0 area 1

R4(config)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
FastEthernet0/0 is up, line protocol is up
  Internet address is 14.14.14.4/24

R4(config)#do sh run | s r o
router ospf 400
 router-id 44.44.44.44
 log-adjacency-changes
 network 14.14.14.4 0.0.0.0 area 0

R5(config)#do sh prot | e do
Global values:
  Internet Protocol routing is enabled
FastEthernet0/0 is up, line protocol is up
  Internet address is 25.25.25.5/24

R5(config)#do sh run | s r o
router ospf 500
 router-id 55.55.55.55
 log-adjacency-changes
 network 25.25.25.5 0.0.0.0 area 0


R1(config)#do sh run int s0/0
Building configuration...

Current configuration : 216 bytes
!
interface Serial0/0
 ip address 12.12.12.1 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-point
 clock rate 2000000
 frame-relay map ip 12.12.12.2 102 broadcast
 no frame-relay inverse-arp
end

R2(config)#do sh run int s0/0
Building configuration...

Current configuration : 216 bytes
!
interface Serial0/0
 ip address 12.12.12.2 255.255.255.0
 encapsulation frame-relay
 ip ospf network point-to-point
 clock rate 2000000
 frame-relay map ip 12.12.12.1 201 broadcast
 no frame-relay inverse-arp
end
!

*********************
* BASIC VERIFICATION *
*********************


R1(config)#do sh ip ro os
     23.0.0.0/24 is subnetted, 1 subnets
O       23.23.23.0 [110/128] via 13.13.13.3, 00:14:28, Serial0/1
     25.0.0.0/24 is subnetted, 1 subnets
O       25.25.25.0 [110/74] via 12.12.12.2, 00:02:29, Serial0/0


R2(config)#do sh ip ro os
     13.0.0.0/24 is subnetted, 1 subnets
O       13.13.13.0 [110/128] via 23.23.23.3, 00:13:26, Serial0/1
     14.0.0.0/24 is subnetted, 1 subnets
O       14.14.14.0 [110/74] via 12.12.12.1, 00:01:52, Serial0/0


R1(config)#do ping 25.25.25.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 25.25.25.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 136/608/1800 ms


R2(config)#do ping 14.14.14.4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 14.14.14.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 352/528/608 ms


R4(config)#do sh ip ro os
     23.0.0.0/24 is subnetted, 1 subnets
O IA    23.23.23.0 [110/138] via 14.14.14.1, 00:02:44, FastEthernet0/0
     25.0.0.0/24 is subnetted, 1 subnets
O       25.25.25.0 [110/84] via 14.14.14.1, 00:03:37, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
O       12.12.12.0 [110/74] via 14.14.14.1, 00:03:37, FastEthernet0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/74] via 14.14.14.1, 00:03:37, FastEthernet0/0


R5(config)#do sh ip ro os
     23.0.0.0/24 is subnetted, 1 subnets
O IA    23.23.23.0 [110/74] via 25.25.25.2, 00:05:33, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
O       12.12.12.0 [110/74] via 25.25.25.2, 00:05:33, FastEthernet0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/138] via 25.25.25.2, 00:05:33, FastEthernet0/0
     14.0.0.0/24 is subnetted, 1 subnets
O       14.14.14.0 [110/84] via 25.25.25.2, 00:05:33, FastEthernet0/0


R4(config)#do ping 25.25.25.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 25.25.25.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 340/416/536 ms


R5(config)#do ping 14.14.14.4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 14.14.14.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 312/528/956 ms

Perfectly cool as R4 and R5 can reach each other's Fast Ethernet Interfaces without any problem.

-------------------------------

Now lets hop on to R1 and shutdown the frame relay link:

R1(config)#int s0/0
R1(config-if)#sh
R1(config-if)#
*Mar  1 01:04:39.507: %OSPF-5-ADJCHG: Process 100, Nbr 22.22.22.22 on Serial0/0 from
FULL to DOWN, Neighbor Down: Interface down or detached
*Mar  1 01:04:41.503: %LINK-5-CHANGED: Interface Serial0/0, changed state to administ
ratively down
*Mar  1 01:04:42.503: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, chan
ged state to down

R1(config)#do sh frame map
Serial0/0 (administratively down): ip 12.12.12.2
              dlci 102(0x66,0x1860), static,
              broadcast,
              CISCO, status deleted


-----------------------------------


Now lets see if R4 can still reach R5:

R4(config)#do ping 25.25.25.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 25.25.25.5, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

R4(config)#do sh ip ro os
     23.0.0.0/24 is subnetted, 1 subnets
O IA    23.23.23.0 [110/138] via 14.14.14.1, 00:03:25, FastEthernet0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/74] via 14.14.14.1, 00:11:32, FastEthernet0/0


Hmmmm....Now lets fix this :-)


But before that in short R4 is not able to reach R5 is because of OSPF rule that we learned in CCNA is that two areas must cross AREA O in order to reach each other. Why that rule is there ? Hmmm .... I have just explained it in my last OSPF post.

But here in our scenario AREA 0 gets split in half . Basically I call it broken AREA 0. If we take a look little deeper the scenario looks like is AREA 0 -> AREA 1 -> AREA 0. Now because of our AREA 0 in center rule we can't directly cross AREA 1 in the middle. So the way we can fix it using a OSPF bandage called OSPF Virtual Link.

So by building a virtual link between R1 and R2 passing through R3 we can fix this issue. So basically by building a virtual link we are extending AREA 0 size. In short "Virtual links are used to extend Area 0 across another area. They also can be thought of as tunnels for LSAs. They are deployed in cases when areas become partitioned or an area does not border Area 0".

*********************************
*          Fixture & Verification             *
*********************************

R1(config)#router ospf 100
R1(config-router)#area 1 virtual-link 22.22.22.22

R2(config)#router ospf 200
R2(config-router)#area 1 virtual-link 11.11.11.11

R1(config-router)#
*Mar  1 01:10:49.811: %OSPF-5-ADJCHG: Process 100, Nbr 22.22.22.22 on OSPF_VL0 from L
OADING to FULL, Loading Done

R2(config-router)#
*Mar  1 01:09:18.335: %OSPF-5-ADJCHG: Process 200, Nbr 11.11.11.11 on OSPF_VL0 from L
OADING to FULL, Loading Done

R4(config)#do ping 25.25.25.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 25.25.25.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 160/283/408 ms


R4(config)#do sh ip ro os
     23.0.0.0/24 is subnetted, 1 subnets
O IA    23.23.23.0 [110/138] via 14.14.14.1, 00:09:14, FastEthernet0/0
     25.0.0.0/24 is subnetted, 1 subnets
O       25.25.25.0 [110/148] via 14.14.14.1, 00:03:04, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
O       12.12.12.0 [110/202] via 14.14.14.1, 00:03:04, FastEthernet0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/74] via 14.14.14.1, 00:17:21, FastEthernet0/0


R1(config)#do sh ip ro os
     23.0.0.0/24 is subnetted, 1 subnets
O       23.23.23.0 [110/128] via 13.13.13.3, 00:22:26, Serial0/1
     25.0.0.0/24 is subnetted, 1 subnets
O       25.25.25.0 [110/138] via 13.13.13.3, 00:05:42, Serial0/1
     12.0.0.0/24 is subnetted, 1 subnets
O       12.12.12.0 [110/192] via 13.13.13.3, 00:05:42, Serial0/1


R2(config)#do sh ip ro os
     13.0.0.0/24 is subnetted, 1 subnets
O       13.13.13.0 [110/128] via 23.23.23.3, 00:45:56, Serial0/1
     14.0.0.0/24 is subnetted, 1 subnets
O       14.14.14.0 [110/138] via 23.23.23.3, 00:08:03, Serial0/1


R3#sh ip ro os
     25.0.0.0/24 is subnetted, 1 subnets
O IA    25.25.25.0 [110/74] via 23.23.23.2, 00:26:34, Serial0/0
     12.0.0.0/24 is subnetted, 1 subnets
O IA    12.12.12.0 [110/128] via 23.23.23.2, 00:26:34, Serial0/0
     14.0.0.0/24 is subnetted, 1 subnets
O IA    14.14.14.0 [110/74] via 13.13.13.1, 00:25:25, Serial0/1

HTH....

DEEPAK ARORA

OSPF Distance Vector Routing Behavior - I thought It's a Link State Routing Protocol :-(

From your past studies of CCNA and CCNP you must always be thinking that OSPF is a Link State Routing Protocol. But now it's time to change that thought :-(

Okay don't afraid as It's not going to be some rocket science stuff :-)

But before that I would like to list ( in short) the difference between "Distance Vector" routing protocols and "Link State" routing protocols.

By definition the Distance vector protocols are based on idea of what we commonly called as " Routing By Rumors" . So no router in the Routing Domain has complete piece of information locally. It just blindly trusts information passed by It's Peer routers. Which is not a good idea sometimes and can create potential routing loops in the network.

On the other hand Link State protocols shares entire information within the routing domain. This important piece of information is stored locally in area called "Link State Database". All the routers in same area (eg OSPF & Level in -> IS-IS) have same copy of database. Apart from this there are several other differences as well and can be found in any good CCNA book.


Now most of CCNA and CCNP books put OSPF under umbrella of Link State Routing Protocol. But let me hurt you little by saying that when we talk about link state routing protocols then IS-IS is the only true link state routing protocol.

Ok...Sorry to hurt that felling but it's true that OSPF is not a true link state routing protocol and that is what I am gonna prove it here with simple topologies.


Now first we will take a look at a OPSF topology containing just 1 AREA and will investigate it's behavior with some show commands. So lets begin:

In this simple topology we have 3 routers - R1, R2 and R3. Now once you will lab this up you will find that under default values, the R1 directly reaches to R3 and is not taking path through R2 to reach R3. Although in it's local database it will have entries for R3 loopback learned from R2 and Directly from R3. So looks like Open Shortest Path First protocol does take the shortest path from R1 to R3's Loopback address.

Hmmm... So we confirm that INTRA AREA OSPF routing is Link State In Nature.


Now lets talk about INTER AREA behavior:

In this topology we are trying to find out if Open Shortest Path First (OSPF) is actually taking shortest path . The routers in question here are R4 and R5. From R4 we will try to Reach R5's loopback (with basic configs - nothing fancy) and will try to find if it goes through R6 (Shortest Path - R4->R6->R5) or if it goes through R4->R2->R1->R3->R5(longer path).


Here are the base configurations for each router:


*************************
*        CONFIGURATION            *
*************************
R1#sh ip int b | e do
Interface                  IP-Address      OK? Method Status   Protocol
Serial0/0                  12.12.12.1      YES manual up          up
Serial0/1                  13.13.13.1      YES manual up          up
Loopback0                  11.11.11.11     YES manual up       up


R1#sh run | s r o
router ospf 1
 log-adjacency-changes
 network 12.12.12.1 0.0.0.0 area 0
 network 13.13.13.1 0.0.0.0 area 0

R2#sh ip int b | e do
Interface                  IP-Address      OK? Method Status   Protocol
Serial0/0                  12.12.12.2      YES manual up           up
Serial0/1                  24.24.24.2      YES manual up           up
Loopback0                  22.22.22.22     YES manual up        up


R2#sh run | s r o
router ospf 1
 log-adjacency-changes
 network 12.12.12.2 0.0.0.0 area 0
 network 24.24.24.2 0.0.0.0 area 2

R3#sh ip int b | e do
Interface                  IP-Address      OK? Method Status  Protocol
Serial0/0                  13.13.13.3      YES manual up         up
Serial0/1                  35.35.35.3      YES manual up         up
Loopback0                  33.33.33.33     YES manual up      up

R3#sh run | s r o
router ospf 1
 log-adjacency-changes
 network 13.13.13.3 0.0.0.0 area 0
 network 35.35.35.3 0.0.0.0 area 3

R4#sh ip int b | e do
Interface                  IP-Address      OK? Method Status     Protocol
Serial0/0                  24.24.24.4      YES manual up            up
Serial0/1                  46.46.46.4      YES manual up            up
Loopback0                  44.44.44.44     YES manual up         up


R4#sh run | s r o
router ospf 1
 log-adjacency-changes
 network 24.24.24.4 0.0.0.0 area 2
 network 44.44.44.44 0.0.0.0 area 2
 network 46.46.46.4 0.0.0.0 area 2


R5#sh ip int b | e unassign|do
Interface                  IP-Address      OK? Method Status  Protocol
Serial0/0                  35.35.35.5      YES manual up          up
Serial0/1                  65.65.65.5      YES manual up          up
Loopback0                  55.55.55.55     YES manual up       up


R5#sh run | s r o
router ospf 1
 log-adjacency-changes
 network 35.35.35.5 0.0.0.0 area 3
 network 55.55.55.55 0.0.0.0 area 3
 network 65.65.65.5 0.0.0.0 area 3


R6#sh ip int b | e do
Interface                  IP-Address      OK? Method Status      Protocol
Serial0/0                  46.46.46.6      YES manual up             up
Serial0/1                  65.65.65.6      YES manual up             up

R6#sh run | s r o
router ospf 1
 log-adjacency-changes
 network 46.46.46.6 0.0.0.0 area 2
 network 65.65.65.6 0.0.0.0 area 3

Now as we are done with basic configuration. Now lets review the routing tables of each router in the topology to find out which path R4 is taking to reach R5's loopback interface.

*************************
*          VERIFICATION             *
*************************

R1#sh ip ro os
     35.0.0.0/24 is subnetted, 1 subnets
O IA    35.35.35.0 [110/128] via 13.13.13.3, 00:40:50, Serial0/1
     55.0.0.0/32 is subnetted, 1 subnets
O IA    55.55.55.55 [110/129] via 13.13.13.3, 00:31:55, Serial0/1
     65.0.0.0/24 is subnetted, 1 subnets
O IA    65.65.65.0 [110/192] via 13.13.13.3, 00:24:11, Serial0/1
     24.0.0.0/24 is subnetted, 1 subnets
O IA    24.24.24.0 [110/128] via 12.12.12.2, 00:49:54, Serial0/0
     46.0.0.0/24 is subnetted, 1 subnets
O IA    46.46.46.0 [110/192] via 12.12.12.2, 00:24:32, Serial0/0
     44.0.0.0/32 is subnetted, 1 subnets
O IA    44.44.44.44 [110/129] via 12.12.12.2, 00:45:28, Serial0/0 


R2#sh ip ro os
     35.0.0.0/24 is subnetted, 1 subnets
O IA    35.35.35.0 [110/192] via 12.12.12.1, 00:41:18, Serial0/0
     55.0.0.0/32 is subnetted, 1 subnets
O IA    55.55.55.55 [110/193] via 12.12.12.1, 00:32:23, Serial0/0
     65.0.0.0/24 is subnetted, 1 subnets
O IA    65.65.65.0 [110/256] via 12.12.12.1, 00:24:39, Serial0/0
     46.0.0.0/24 is subnetted, 1 subnets
O       46.46.46.0 [110/128] via 24.24.24.4, 00:25:01, Serial0/1
     13.0.0.0/24 is subnetted, 1 subnets
O       13.13.13.0 [110/128] via 12.12.12.1, 00:50:29, Serial0/0
     44.0.0.0/32 is subnetted, 1 subnets
O       44.44.44.44 [110/65] via 24.24.24.4, 00:45:57, Serial0/1


R3#sh ip ro os
     55.0.0.0/32 is subnetted, 1 subnets
O       55.55.55.55 [110/65] via 35.35.35.5, 00:32:43, Serial0/1
     65.0.0.0/24 is subnetted, 1 subnets
O       65.65.65.0 [110/128] via 35.35.35.5, 00:24:59, Serial0/1
     24.0.0.0/24 is subnetted, 1 subnets
O IA    24.24.24.0 [110/192] via 13.13.13.1, 00:41:43, Serial0/0
     12.0.0.0/24 is subnetted, 1 subnets
O       12.12.12.0 [110/128] via 13.13.13.1, 00:41:43, Serial0/0
     46.0.0.0/24 is subnetted, 1 subnets
O IA    46.46.46.0 [110/256] via 13.13.13.1, 00:25:20, Serial0/0
     44.0.0.0/32 is subnetted, 1 subnets
O IA    44.44.44.44 [110/193] via 13.13.13.1, 00:41:43, Serial0/0


R4#sh ip ro os
     35.0.0.0/24 is subnetted, 1 subnets
O IA    35.35.35.0 [110/256] via 24.24.24.2, 00:28:30, Serial0/0
     55.0.0.0/32 is subnetted, 1 subnets
O IA    55.55.55.55 [110/257] via 24.24.24.2, 00:28:30, Serial0/0
     65.0.0.0/24 is subnetted, 1 subnets
O IA    65.65.65.0 [110/320] via 24.24.24.2, 00:25:28, Serial0/0
     12.0.0.0/24 is subnetted, 1 subnets
O IA    12.12.12.0 [110/128] via 24.24.24.2, 00:28:30, Serial0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/192] via 24.24.24.2, 00:28:30, Serial0/0


R5#sh ip ro os
     24.0.0.0/24 is subnetted, 1 subnets
O IA    24.24.24.0 [110/256] via 35.35.35.3, 00:29:01, Serial0/0
     12.0.0.0/24 is subnetted, 1 subnets
O IA    12.12.12.0 [110/192] via 35.35.35.3, 00:29:01, Serial0/0
     46.0.0.0/24 is subnetted, 1 subnets
O IA    46.46.46.0 [110/320] via 35.35.35.3, 00:26:12, Serial0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/128] via 35.35.35.3, 00:29:01, Serial0/0
     44.0.0.0/32 is subnetted, 1 subnets
O IA    44.44.44.44 [110/257] via 35.35.35.3, 00:29:01, Serial0/0



R6#sh ip ro os
     35.0.0.0/24 is subnetted, 1 subnets
O       35.35.35.0 [110/128] via 65.65.65.5, 00:25:26, Serial0/1
     55.0.0.0/32 is subnetted, 1 subnets
O       55.55.55.55 [110/65] via 65.65.65.5, 00:25:27, Serial0/1
     24.0.0.0/24 is subnetted, 1 subnets
O       24.24.24.0 [110/128] via 46.46.46.4, 00:25:45, Serial0/0
     12.0.0.0/24 is subnetted, 1 subnets
O IA    12.12.12.0 [110/192] via 46.46.46.4, 00:25:45, Serial0/0
     13.0.0.0/24 is subnetted, 1 subnets
O IA    13.13.13.0 [110/192] via 65.65.65.5, 00:25:27, Serial0/1
     44.0.0.0/32 is subnetted, 1 subnets
O       44.44.44.44 [110/65] via 46.46.46.4, 00:25:45, Serial0/0

So as you can see R4 is taking longer path instead of taking short path through Router R6. So technically it proves the point that Inter-Area OSPF routing is Distance vector in nature. However this behavior protects OSPF from forming routing loops when LSA 3 gets exchanged between different areas. So inter-area topology works more like a Hub-n-Spoke topology where OSPF area 0 acts as HUB and rest of areas acts as SPOKE.

But before I end, I want to share Database of R5 and R6. Just make sure you look and understand R6's Databse because there is something very important to see in there :-)

*************************
*      Database Verification       *
*************************

R5#sh ip o d

            OSPF Router with ID (65.65.65.5) (Process ID 1)

                Router Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum Link count
33.33.33.33     33.33.33.33     419         0x80000005 0x0013E4 2
65.65.65.5      65.65.65.5      42          0x80000007 0x00CEFE 5
65.65.65.6      65.65.65.6      1885        0x80000001 0x00B703 2

                Summary Net Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.0      33.33.33.33     920         0x80000002 0x00F81A
13.13.13.0      33.33.33.33     920         0x80000002 0x0052FD
24.24.24.0      33.33.33.33     920         0x80000002 0x00C9E4
44.44.44.44     33.33.33.33     920         0x80000002 0x0047FD
46.46.46.0      33.33.33.33     1951        0x80000001 0x0032FA


R6#sh ip o d

            OSPF Router with ID (65.65.65.6) (Process ID 1)

                Router Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Link count
22.22.22.22     22.22.22.22     1579        0x80000005 0x00B5F5 2
44.44.44.44     44.44.44.44     1939        0x80000008 0x00F714 5
65.65.65.6      65.65.65.6      1938        0x80000001 0x001E27 2

                Summary Net Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.0      22.22.22.22     1579        0x80000002 0x00C1BD
13.13.13.0      22.22.22.22     1579        0x80000002 0x00201C
35.35.35.0      22.22.22.22     1078        0x80000002 0x008732
55.55.55.55     22.22.22.22     590         0x80000002 0x0096AE
65.65.65.0      22.22.22.22     67          0x80000002 0x00CC52

                Router Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum Link count
33.33.33.33     33.33.33.33     456         0x80000005 0x0013E4 2
65.65.65.5      65.65.65.5      79          0x80000007 0x00CEFE 5
65.65.65.6      65.65.65.6      1921        0x80000001 0x00B703 2

                Summary Net Link States (Area 3)

Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.0      33.33.33.33     959         0x80000002 0x00F81A
13.13.13.0      33.33.33.33     959         0x80000002 0x0052FD
24.24.24.0      33.33.33.33     959         0x80000002 0x00C9E4
44.44.44.44     33.33.33.33     959         0x80000002 0x0047FD
46.46.46.0      33.33.33.33     1989        0x80000001 0x0032FA 

Now if you want to dig in theory of this further more, please visit Jeff Doyle's blog: 
http://www.networkworld.com/community/node/19293 

HTH

 Deepak Arora 

MPLS 101 - V Lecture From IP Expert CCIE Marko

http://ipexpert.acrobat.com/p75978952/

HTH

Deepak Arora

Frame-Relay Switching

So today I wanna talk about "Nasty Frame-Relay Switching Stuff". I mean if you are a CCIE R&S Version 4 student then you need to know this stuff now. In Ver 3 blueprint the FR Switch in lab was always preconfigured. Although there were some Pitfalls associated with those initial configurations to test your Frame-Relay skills like some extra DLCIs configured which were not required or in other words to add some more fun into section like OSPF over FR.

 Take a look at diagram below. Here routers R1, R2 & R3 are connected to another router in middle which is acting as a Frame-Relay Switch < :-) Yes you can configure even a router as a Frame-Relay Switch>. R1 is acting as Hub and connected to R2/R3 which are acting as Spoke Routers. Also there is no Direct DLCI between R2 & R3.

Now lets hop on to the command line and review the necessary configuration required on each device. Later we will discuss the theory along with some verification stuff.

R1#
!
interface Serial1/0
 ip address 10.0.0.1 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.0.0.1 103
 frame-relay map ip 10.0.0.3 103 broadcast
 frame-relay map ip 10.0.0.2 102 broadcast
 no frame-relay inverse-arp
 !
--------------------------------------
R2#
!
interface Serial1/0
 ip address 10.0.0.2 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.0.0.2 201
 frame-relay map ip 10.0.0.3 201
 frame-relay map ip 10.0.0.1 201 broadcast
 no frame-relay inverse-arp
 !
--------------------------------------
R3#
!
interface Serial1/0
 ip address 10.0.0.3 255.255.255.0
 encapsulation frame-relay
 serial restart-delay 0
 frame-relay map ip 10.0.0.3 301
 frame-relay map ip 10.0.0.2 301
 frame-relay map ip 10.0.0.1 301 broadcast
 no frame-relay inverse-arp
 !
--------------------------------------
Now lets take a look at FRswitch configuration and discuss little bit about it:


FRswitch#
!
interface Serial1/0
 no ip address -> No IP address needs to be configured
 encapsulation frame-relay ->Enabling WAN Encapsulation FR
 logging event subif-link-status ->Optional
 logging event dlci-status-change ->Optional
 serial restart-delay 0
 clock rate 64000 -> Setting Up clock rate on DCE side
 no frame-relay inverse-arp
 frame-relay intf-type dce -> Configuring FR interface as DCE type
 frame-relay route 102 interface Serial1/1 201 ->If Data received on DLCI 102 then it will be sent over to interface serial1/1 over DLCI 201 <- Mapping Incoming DLCI to Outgoing DLCI ->
 frame-relay route 103 interface Serial1/2 301 ->Same Logic as explained above
 !
!
interface Serial1/1
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 64000
 no frame-relay inverse-arp
 frame-relay intf-type dce
 frame-relay route 201 interface Serial1/0 102
 !
!
interface Serial1/2
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 64000
 no frame-relay inverse-arp
 frame-relay intf-type dce
 frame-relay route 301 interface Serial1/0 103
 !

So all frame relay switch doing is routing traffic at layer 2. It's more like Air traffic controller guy who knows if a plane comes on certain track then he has to route it to another predefined track. Of course "No chances for error" there

Now lets do the verification:


FRswitch#sh frame route
Input Intf      Input Dlci      Output Intf     Output Dlci     Status
Serial1/0       102             Serial1/1       201             active
Serial1/0       103             Serial1/2       301             active
Serial1/1       201             Serial1/0       102             active
Serial1/2       301             Serial1/0       103             active


R1#sh frame map
Serial1/0 (up): ip 10.0.0.2 dlci 102(0x66,0x1860), static,
              broadcast,
              CISCO, status defined, active
Serial1/0 (up): ip 10.0.0.1 dlci 103(0x67,0x1870), static,
               broadcast,
              CISCO, status defined, active
Serial1/0 (up): ip 10.0.0.3 dlci 103(0x67,0x1870), static,
              broadcast,
              CISCO, status defined, active


R2#sh frame map
Serial1/0 (up): ip 10.0.0.2 dlci 201(0xC9,0x3090), static,
              CISCO, status defined, active
Serial1/0 (up): ip 10.0.0.3 dlci 201(0xC9,0x3090), static,
              CISCO, status defined, active
Serial1/0 (up): ip 10.0.0.1 dlci 201(0xC9,0x3090), static,
              broadcast,
              CISCO, status defined, active


R3#sh frame map
Serial1/0 (up): ip 10.0.0.3 dlci 301(0x12D,0x48D0), static,
              CISCO, status defined, active
Serial1/0 (up): ip 10.0.0.2 dlci 301(0x12D,0x48D0), static,
              CISCO, status defined, active
Serial1/0 (up): ip 10.0.0.1 dlci 301(0x12D,0x48D0), static,
              broadcast,
              CISCO, status defined, active


R2#ping 10.0.0.1 r 1

Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
!
Success rate is 100 percent (1/1), round-trip min/avg/max = 160/160/160 ms
R2#ping 10.0.0.2 r 1

Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 10.0.0.2, timeout is 2 seconds:
!
Success rate is 100 percent (1/1), round-trip min/avg/max = 624/624/624 ms
R2#ping 10.0.0.3 r 1

Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 10.0.0.3, timeout is 2 seconds:
!
Success rate is 100 percent (1/1), round-trip min/avg/max = 536/536/536 ms
R2#

Best Regards,

Deepak Arora

V Lecture On BGP - From Ndiaye Malick

Part 1: http://classroom.internetworkexpert.com/p87301619/
Part 2: http://classroom.internetworkexpert.com/p85611450/

Rgds,

Deepak Arora