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Archive for November, 2011

Bridging for me is simply straightforward here in Bridging we are NOT rewriting the Layer 3 packet simply forwarding  the Layer 3 information in Layer 2 frame intact from one end to other.

Today we are discussing Bridging same subnet over the WAN links , however i have taken the subnet in different VLANs just for fun to prove the reachability not depends on the local VLANs used in the LAN atmosphere.

Here i have assigned 192.168.10.1/24 to PC-1 and this is in VLAN 10 , altogether the other side PC-2 ip add is 192.168.10.2/24 and this is in VLAN 20.

We are using IRB (Integrated Routing and Bridging) for this.It mean we can Bridge and Route at the same time on the same interface.

On Router-1 and Router-2

bridge irb
bridge 1 protocol ieee
bridge 1 route ip

Then we assign appropriate interfaces into “bidge-group 1” on R1 and R2.

R1(config)#int fa0/0
R1(config-if)#bridge-group 1
R1(config-if)#int s0/0
R1(config-if)#bridge-group 1
R1(config-if)#end

R2(config)#int fa0/0
R2(config-if)#bridge-group 1
R2(config-if)#int s0/0
R2(config-if)#bridge-group 1
R2(config-if)#end

Then we will create a Virtual BVI interface on R1 and R2 to talk to the routed Serial interface and assign the ip range used as default-gateway for PC-1 and PC-2.
R1(config)#int bvi 1
R1(config-if)#ip add 192.168.10.254 255.255.255.0
R1(config-if)#end
R1#

R2(config)#int bvi 1
R2(config-if)#ip add 192.168.10.253 255.255.255.0
R2(config-if)#end
R2#

Other relevant configs are simple not any fancy stuffs used.

PC-1#sh ip route
Default gateway is 192.168.10.254
PC-2#sh ip route
Default gateway is 192.168.10.253

PC-1#sh run int fa0/0
interface FastEthernet0/0
ip address 192.168.10.1 255.255.255.0
no ip route-cache
duplex auto
speed auto
end

PC-2#sh run int fa0/0
interface FastEthernet0/0
ip address 192.168.10.2 255.255.255.0
no ip route-cache
duplex auto
speed auto
end

We will wait for some time for MAC address learning purpose and issue the command ” show bridge 1 verbose ” on R1 and R2 , this is very helpful command in Bridging Scenarios.

R1#sh bridge 1 verbose

Total of 300 station blocks, 297 free
Codes: P – permanent, S – self

BG Hash      Address      Action  Interface      VC    Age   RX count   TX count
1 00/0   c201.080a.0000 forward  Serial0/0       –      2         11          9
1 00/1   c205.080a.0000 forward  Serial0/0       –      1         13         10
1 00/2   c204.080a.0000 forward  FastEthernet0/0 –      1         26         18

Flood ports (BG 1)           RX count    TX count
FastEthernet0/0                     3           3
Serial0/0                           3           3

The configuration look healthy so far let us check the other side R2.

R1#sh arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.10.1            8   c204.080a.0000  ARPA   BVI1
Internet  192.168.10.254          –   c200.080a.0000  ARPA   BVI1

R2#sh bridge 1 verbose

Total of 300 station blocks, 297 free
Codes: P – permanent, S – self

BG Hash      Address      Action  Interface      VC    Age   RX count   TX count
1 00/0   c200.080a.0000 forward  Serial0/0       –      4          5          4
1 00/1   c205.080a.0000 forward  FastEthernet0/0 –      3         19         14
1 00/2   c204.080a.0000 forward  Serial0/0       –      3         20         15

Flood ports (BG 1)           RX count    TX count
FastEthernet0/0                     3           3
Serial0/0                           3           3

R2#sh arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.10.2            9   c205.080a.0000  ARPA   BVI1
Internet  192.168.10.253          –   c201.080a.0000  ARPA   BVI1

Here also it looks we are learning MAC addresses from port FastEthernet 0/0 and Serial 0/0 , lets run our final verification command from PC-1 altogether over the WAN links crossing R1 and R2 over the other side PC-2.

PC-1#ping 192.168.10.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.10.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/15/32 ms

PC-2#trace 192.168.10.1

Type escape sequence to abort.
Tracing the route to 192.168.10.1

1 192.168.10.1 44 msec *  20 msec

Indeed we are successful in Bridging LAN over the WAN.

Happy Bridging the Love across Borders :)

Here i have taken a simple topology R1 is connecting directly over Serial 0/0 link to BB1 , and as we know we dont have much access to Backbone routers in LAB , what if we dont know the EIGRP AS number of Neighbouring router.

R1 ——S0/0———BB1

The ip address used between R1 and BB1 is in range of 200.200.200.0/30

Lets start R1 by configuring it in AS 100 (wild guess) .

R1(config-if)#router eigrp 100
R1(config-router)#no auto
R1(config-router)#netw 0.0.0.0
R1(config-router)#end

It seems we are not lucky so the neighborship is still down , lets see the output of “sh ip protocols”.

R1#sh ip protocols
Routing Protocol is “eigrp 100”
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Redistributing: eigrp 100
EIGRP NSF-aware route hold timer is 240s
Automatic network summarization is not in effect
Maximum path: 4
Routing for Networks:
0.0.0.0
Routing Information Sources:
Gateway         Distance      Last Update
Distance: internal 90 external 170

Here also it seems everything fine , so here starts our troubleshooting we will use Extended Access list 101 to limit the output of “debug ip packet details 101”

R1(config)#access-list 101 permit ip any host 224.0.0.10

R1#debug ip packet detail 101
IP packet debugging is on (detailed) for access list 101

*Mar  1 00:07:39.131: IP: s=200.200.200.1 (local), d=224.0.0.10 (Serial0/0), len 60, sending broad/multicast, proto=88
*Mar  1 00:07:39.219: IP: s=200.200.200.2 (Serial0/0), d=224.0.0.10, len 60, rcvd 2, proto=88

The output of the debug shows that we indeed sending and receiving Eigrp updates on IP protocol 88 port.But why our neighbor is still down and answer is we are in wrong EIGRP AS , so the Question is how do we figure out the correct EIGRP AS number of the neighbouring router BB1.

Here is the trick.

We use a hidden command in debug called as “DUMP” feature it will show the HEX characters received from the neighbouring router.

R1#debug ip packet detail 101 dump
IP packet debugging is on (detailed) (dump) for access list 101
R1#
*Mar  1 00:12:05.643: IP: s=200.200.200.2 (Serial0/0), d=224.0.0.10, len 60, rcvd 2, proto=88
07DFE7F0:          0F000800 45C0003C 00000000
07DFE800: 015847D5 C8C8C802 E000000A 0205DF27
07DFE810: 00000000 00000000 00000000 00000FA5

07DFE820: 0001000C 01000100 0000000F 00040008  …………….
07DFE830: 0C040102                             ….
*Mar  1 00:12:07.747: IP: s=200.200.200.1 (local), d=224.0.0.10 (Serial0/0), len 60, sending broad/multicast, proto=88

Here in the first highlighted part E000000A , if we translate this into binary it comes 224.0.0.10 the multicast address of the EIGRP , then we move five steps ahead of this HEX character we see 00000FA5 and this is our neighouring router AS number , we convert this HEX number into binary it comes “4005” and that is our AS number of the BB1.

Lets not assume and configure R1 with AS 4005 and see what results we see.

R1(config)#no router eigrp 100
R1(config)#router eigrp 4005
R1(config-router)#no auto
R1(config-router)#netw 0.0.0.0
R1(config-router)#
*Mar  1 00:23:39.883: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 4005: Neighbor 200.200.200.2 (Serial0/0) is up: new adjacency

So now it is confirmed that the BB1 AS number is 4005.