Tracking ip routing instead of interface line protocol

August 22, 2008 at 2:39 pm | Posted in IP Services | Leave a comment

When the WAN interface are virtual one, such as Dialer, Tunnel, the interface does not go down even if the WAN status actually inactive (i.e. physical interface down, or PPP session is down).

In this case, we should use object tracking instead of interface tracking, to track not only the line protocol status (up/down), but also whether routing can be done via that interface (i.e should there be a connected route via that interface when we do “show ip route connected”). For a more accurate reachability status via that interface, we can do IP SLA to track ping reachibility to backbone.

In a specific scenario of SHDSL and ADSL using PPP over dialer interface, tracking ip routing is good enough. Here’s the sample config (need to replace Serial interface with Dialer)

Configuration

R1#

interface Serial1/1
ip address negotiated
encapsulation ppp

track 100 interface Serial1/1 ip routing

interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.0
standby 1 ip 10.1.1.254
standby 1 priority 105
standby 1 preempt
standby 1 track 100

standby 2 ip 10.1.1.253
standby 2 preempt
standby 2 track 100

R2#

interface Serial1/1
ip address 23.0.0.2 255.255.255.0
encapsulation ppp

track 100 interface Serial1/1 ip routing

interface FastEthernet0/0
ip address 10.1.1.2 255.255.255.0
standby 1 ip 10.1.1.254
standby 1 preempt
standby 1 track 100

standby 2 ip 10.1.1.253
standby 2 priority 105
standby 2 preempt
standby 2 track 100

R3#

interface Serial1/2
ip address 13.0.0.3 255.255.255.0
encapsulation ppp
! to assign IP address to PPP peer dynamically
peer default ip address 13.0.0.1

interface Serial1/3
ip address 23.0.0.3 255.255.255.0
encapsulation ppp

Verification:

We simulate PPP negotiation failure, by removing WAN IP dynamically via PPP. Note that the interface is still up, but object tracking already kicks in! Interface tracking will not overcome this situation

R1#sh ip int brief | ex unass
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            10.1.1.1        YES manual up                    up
R1#sh ip int brief | in up
FastEthernet0/0            10.1.1.1        YES manual up                    up
Serial1/1                  unassigned      YES IPCP   up                    up

R1#show track 100
Track 100
Interface Serial1/1 ip routing
IP routing is Down (no ip addr)
4 changes, last change 00:16:06
Tracked by:
HSRP FastEthernet0/0 1
HSRP FastEthernet0/0 2

R1#show standby
FastEthernet0/0 – Group 1
State is Standby
6 state changes, last state change 00:16:14
Virtual IP address is 10.1.1.254
Active virtual MAC address is 0000.0c07.ac01
Local virtual MAC address is 0000.0c07.ac01 (v1 default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.604 secs
Preemption enabled
Active router is 10.1.1.2, priority 100 (expires in 9.440 sec)
Standby router is local
Priority 95 (configured 105)
Track interface Serial1/1 state Up decrement 10
Track object 100 state Down decrement 10
IP redundancy name is “hsrp-Fa0/0-1” (default)
FastEthernet0/0 – Group 2
State is Standby
4 state changes, last state change 00:23:06
Virtual IP address is 10.1.1.253
Active virtual MAC address is 0000.0c07.ac02
Local virtual MAC address is 0000.0c07.ac02 (v1 default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.516 secs
Preemption enabled
Active router is 10.1.1.2, priority 105 (expires in 7.968 sec)
Standby router is local
Priority 90 (default 100)
Track object 100 state Down decrement 10
IP redundancy name is “hsrp-Fa0/0-2” (default)

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