Integrated Routing and Bridging Example

Here follows an example of IRB, that will probably make our understanding about this topic a bit easier. This scenario  was based in the Video on Demand from IPExpert CCIE R&S Blended Learning Solutions. A full video dedicated just to it is available in there, and I recommend you to check it out! It rocks! :)

Take a look at the topology:

Those VLANs (VLAN2 and VLAN3) will be bridged through our serial link.

In order to do that, we need to:

1. Create the Bridge-Group;
2. Assign this Bridge-Group to our Interfaces;
3. Create the BVI Interface and assigns an IP Address to it;
4. Create our rules (specifically tell this particular Bridge- Group to Route IP) .

First... what is the function of a "Bridge-Group" ?! Well "Bridge-Group" job is to take  packets to an unknow destination and flood them out any available ports, or more important, to learn were those available ports are for each them.

The catch is, the router can do routing,  can do bridging, but in other to do both, like some interfaces to route, some interfaces to bridge we need to use IRB (Integrated Routing and Bridging).

Take a look in the configuration for all devices involved, interfaces FastEthernet0/0 and Serial1/1 in our routers R2 and R3 were assigned to Bridge-Group 1, all interfaces between the origin and destination will be "bridged", the IP Address will be assigned to the BVI Interface, take a look:

R2: int f0/0 bridge-group 1 no shut ! int s1/1  bridge-group 1 no shut ! bridge irb bridge 1 protocol ieee bridge 1 route ip ! int bvi 1 ip address 111.111.111.2 255.255.255.0 no shut R3: int f0/0 bridge-group 1 no shut ! int s1/1 bridge-group 1 no shut ! bridge irb bridge 1 protocol ieee bridge 1 route ip ! int bvi 1 ip address 111.111.111.3 255.255.255.0 no shut SW2 int f1/2 switchport access vlan 2 no shut ! int vlan 2 ip address 111.111.111.22 255.255.255.0 no shut exit SW3 int f1/3 switchport access vlan 3 no shut ! int vlan 3 ip address 111.111.111.33 255.255.255.0 no shut exit

To make double-sure about our IP assignment, we can use the show ip int brief command:

R2#sh ip int brief Interface       IP-Address    OK? Method Status      Protocol FastEthernet0/0 unassigned    YES unset  up          up Serial1/0       unassigned    YES unset administrat. down down Serial1/1       unassigned    YES manual up          up BVI1            111.111.111.2 YES manual up          up R3#sh ip int brief Interface       IP-Address    OK? Method Status      Protocol FastEthernet0/0 unassigned    YES unset  up          up Serial1/0       unassigned    YES unset  administrat. down down Serial1/1       unassigned    YES manual up          up BVI1            111.111.111.3 YES manual up          up

Everything looks good, BVI interface has it´s IP Addresses, and both FastEthernet and Serial interfaces don´t!

Using the command show bridge 1 verbose we can check which interfaces belongs to this specific Bridge-Group:

R2#sh bridge 1 verbose Flood ports (BG 1)           RX count    TX count FastEthernet0/0                     0           0 Serial1/1                           0           0

Seens fine too! So, what next?! Testing! How?! Ping!!!

R2#ping 111.111.111.22 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.22, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 28/68/128 ms R2#ping 111.111.111.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 28/58/136 ms R2#ping 111.111.111.33 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.33, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 60/83/140 ms --------------- R3#ping 111.111.111.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/65/128 ms R3#ping 111.111.111.22 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.22, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 44/88/144 ms R3#ping 111.111.111.33 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.33, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/58/120 ms --------------- SW2#ping 111.111.111.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/64/136 ms SW2#ping 111.111.111.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/95/184 ms SW2#ping 111.111.111.33 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.33, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 80/127/200 ms --------------- SW3#ping 111.111.111.3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.3, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 32/72/124 ms SW3#ping 111.111.111.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 48/105/164 ms SW3#ping 111.111.111.22 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 111.111.111.22, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 92/145/224 ms

Now we have reachability between the two vlans! We can use the command show bridge 1 verbose again to check  the counters and the interfaces involved in this particular bridge group:

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   cc02.09c0.0000 forward  Serial1/1       -  3  10   9 1 00/1   cc05.0f10.0000 forward  Serial1/1       -  1  25  24 1 00/2   cc04.0f10.0000 forward  FastEthernet0/0 -  1  30  28 Flood ports (BG 1)           RX count    TX count FastEthernet0/0                     7           0 Serial1/1                           0           7 R3#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   cc04.0f10.0000 forward  Serial1/1       -  2  20   19 1 00/1   cc01.09c0.0000 forward  Serial1/1       -  0  15   14 1 00/2   cc05.0f10.0000 forward  FastEthernet0/0 -  0  35   33 Flood ports (BG 1)           RX count    TX count FastEthernet0/0                     6           0 Serial1/1                           0           0

Just for curiosity, show arp at R3...

R3#sh arp Protocol  Address     Age (min)  Hardware Addr   Type   Interface Internet  111.111.111.33        5   cc05.0f10.0000  ARPA   BVI1 Internet  111.111.111.3         -   cc02.09c0.0000  ARPA   BVI1 Internet  111.111.111.2         5   cc01.09c0.0000  ARPA   BVI1 Internet  111.111.111.22        5   cc04.0f10.0000  ARPA   BVI1

...and show arp at SW2:

SW2#sh arp Protocol  Address     Age (min)  Hardware Addr   Type   Interface Internet  111.111.111.33        6   cc05.0f10.0000  ARPA   Vlan2 Internet  111.111.111.3         6   cc02.09c0.0000  ARPA   Vlan2 Internet  111.111.111.2         7   cc01.09c0.0000  ARPA   Vlan2 Internet  111.111.111.22        -   cc04.0f10.0000  ARPA   Vlan2

As you can see, everything is working fine! I do recommend you to check IPExpert Bridging Videos, and also Cisco DocCD for more information!

Follows some usefull links:

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_tech_note09186a0080094663.shtml

http://www.cisco.com/en/US/docs/ios/bridging/configuration/guide/br_transprnt_brdg_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1003018