First hop redundancy protocol details

August 21, 2008 at 1:58 pm | Posted in Blogroll, IP Services | Leave a comment

The protocol details are required when we need to use ACL to specifically allow/deny traffic. HSRP and GLBP are Cisco protocols that use UDP, whereas VRRP is open standard that uses its own protocol 112.

HSRP uses multicast UDP port 1985 (both source/destination) to address 224.0.0.2 .

Both active and standby routers send to the multicast address every 3 sec by default.

R1#sh run int fa0/0
interface FastEthernet0/0
ip address 135.0.0.1 255.255.255.0
standby 1 ip 135.0.0.100

R1#debug ip packet detail
IP packet debugging is on (detailed)

Aug 21 12:28:02.571: IP: s=135.0.0.1 (local), d=224.0.0.2 (FastEthernet0/0), len 48, sending broad/multicast
Aug 21 12:28:02.575:     UDP src=1985, dst=1985
Aug 21 12:28:04.155: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.2, len 48, rcvd 0
Aug 21 12:28:04.159:     UDP src=1985, dst=1985
Aug 21 12:28:05.579: IP: s=135.0.0.1 (local), d=224.0.0.2 (FastEthernet0/0), len 48, sending broad/multicast
Aug 21 12:28:05.583:     UDP src=1985, dst=1985

VRRP use its own transport protocol 112 sent to address 224.0.0.18.
Also, notice that only Master router multicasts its status out (every 1 sec by default). The backup passively listens to the multicast address 224.0.0.18 and will take the Master role if it does not hear from the Master.

R1#sh run int fa0/0
interface FastEthernet0/0
ip address 135.0.0.1 255.255.255.0
vrrp 1 ip 135.0.0.100

R1#sh vrrp int fa0/0
FastEthernet0/0 – Group 1
State is Backup
Virtual IP address is 135.0.0.100
Virtual MAC address is 0000.5e00.0101
Advertisement interval is 1.000 sec
Preemption enabled
Priority is 100
Master Router is 135.0.0.3, priority is 100
Master Advertisement interval is 1.000 sec
Master Down interval is 3.609 sec (expires in 3.493 sec)

R1#debug ip packet detail
IP packet debugging is on (detailed)

Aug 21 12:30:50.463: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.18, len 40, rcvd 2, proto=112
Aug 21 12:30:51.431: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.18, len 40, rcvd 2, proto=112
Aug 21 12:30:52.363: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.18, len 40, rcvd 2, proto=112
Aug 21 12:30:53.347: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.18, len 40, rcvd 2, proto=112

R3(config)#int fa0/0
R3(config-if)#shut

R1#sh vrrp
FastEthernet0/0 – Group 1
State is Master
Virtual IP address is 135.0.0.100
Virtual MAC address is 0000.5e00.0101
Advertisement interval is 1.000 sec
Preemption enabled
Priority is 100
Master Router is 135.0.0.1 (local), priority is 100
Master Advertisement interval is 1.000 sec
Master Down interval is 3.609 sec

Aug 21 12:37:10.059: IP: s=135.0.0.1 (local), d=224.0.0.18 (FastEthernet0/0), len 40, sending broad/multicast, proto=112
Aug 21 12:37:10.875: IP: s=135.0.0.1 (local), d=224.0.0.18 (FastEthernet0/0), len 40, sending broad/multicast, proto=112
Aug 21 12:37:11.767: IP: s=135.0.0.1 (local), d=224.0.0.18 (FastEthernet0/0), len 40, sending broad/multicast, proto=112
Aug 21 12:37:12.707: IP: s=135.0.0.1 (local), d=224.0.0.18 (FastEthernet0/0), len 40, sending broad/multicast, proto=112
Aug 21 12:37:13.635: IP: s=135.0.0.1 (local), d=224.0.0.18 (FastEthernet0/0), len 40, sending broad/multicast, proto=112

GLBP uses multicast UDP port 3222 (both source/destination) to address 224.0.0.102 . Both active and standby routers send to the multicast address every 3 sec by default.

R1#
interface FastEthernet0/0
ip address 135.0.0.1 255.255.255.0
glbp 1 ip 135.0.0.100

R1#sh glbp active
FastEthernet0/0 – Group 1
State is Active
2 state changes, last state change 00:02:25
Virtual IP address is 135.0.0.100
Hello time 3 sec, hold time 10 sec
Next hello sent in 1.868 secs
Redirect time 600 sec, forwarder time-out 14400 sec
Preemption disabled
Active is local
Standby is 135.0.0.3, priority 100 (expires in 7.544 sec)
Priority 100 (default)
Weighting 100 (default 100), thresholds: lower 1, upper 100
Load balancing: round-robin
Group members:
c200.067c.0000 (135.0.0.1) local
c202.067c.0000 (135.0.0.3)
There are 2 forwarders (1 active)
Forwarder 1
State is Active
1 state change, last state change 00:02:15
MAC address is 0007.b400.0101 (default)
Owner ID is c200.067c.0000
Redirection enabled
Preemption enabled, min delay 30 sec
Active is local, weighting 100
Arp replies sent: 2
Forwarder 2
State is Listen
MAC address is 0007.b400.0102 (learnt)
Owner ID is c202.067c.0000
Redirection enabled, 597.048 sec remaining (maximum 600 sec)
Time to live: 14397.044 sec (maximum 14400 sec)
Preemption enabled, min delay 30 sec
Active is 135.0.0.3 (primary), weighting 100 (expires in 7.040 sec)

R1#sh glbp brief
Interface   Grp  Fwd Pri State    Address         Active router   Standby router
Fa0/0       1    –   100 Active   135.0.0.100     local           135.0.0.3
Fa0/0       1    1   –   Active   0007.b400.0101  local           –
Fa0/0       1    2   –   Listen   0007.b400.0102  135.0.0.3       –

R1#debug ip packet detail
IP packet debugging is on (detailed)

Aug 21 12:46:45.667: IP: s=135.0.0.1 (local), d=224.0.0.102 (FastEthernet0/0), len 88, sending broad/multicast
Aug 21 12:46:45.671:     UDP src=3222, dst=3222
Aug 21 12:46:47.335: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.102, len 88, rcvd 2
Aug 21 12:46:47.339:     UDP src=3222, dst=3222
Aug 21 12:46:48.675: IP: s=135.0.0.1 (local), d=224.0.0.102 (FastEthernet0/0), len 88, sending broad/multicast
Aug 21 12:46:48.679:     UDP src=3222, dst=3222
Aug 21 12:46:50.339: IP: s=135.0.0.3 (FastEthernet0/0), d=224.0.0.102, len 88, rcvd 2
Aug 21 12:46:50.343:     UDP src=3222, dst=3222

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