From: Huan Pham (pnhuan@yahoo.com)
Date: Mon Nov 10 2008 - 11:14:48 ARST
More testing results, missing from previous post.
When R6 dies, i try to ping 155.1.45.4 (which is another interface of R4). If
R1 knew to turn to backup default gateway, the ping should have been
sucessfull. But this is not the case.
Rack1R1#ping 155.1.146.255
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.146.255, timeout is 2 seconds:
Reply to request 0 from 155.1.146.4, 4 ms
Reply to request 1 from 155.1.146.4, 1 ms
Reply to request 2 from 155.1.146.4, 1 ms
Reply to request 3 from 155.1.146.4, 1 ms
Reply to request 4 from 155.1.146.4, 1 ms
Rack1R1#
Rack1R1#ping 155.1.45.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.45.4, timeout is 2 seconds:
..
Success rate is 0 percent (0/2)
Rack1R1#sh ip route
Default gateway is 155.1.146.6
Host Gateway Last Use Total Uses Interface
ICMP redirect cache is empty
Rack1R1#trace 155.1.45.4
Type escape sequence to abort.
Tracing the route to 155.1.45.4
1 *
--- On Mon, 11/10/08, Huan Pham <pnhuan@yahoo.com> wrote:
From: Huan Pham <pnhuan@yahoo.com>
Subject: IOS DHCP server - how to test assigned backup default gateway?
To: "CCIE Lab" <ccielab@groupstudy.com>
Date: Monday, November 10, 2008, 11:47 PM
Hi GS,
The IOS DHCP server feature allows us to specify up to 8 default gateways, in
order of preference. My question are:
- How DHCP clients keep track of the the primary default gateway, so that when
it dies, clients can switch to the backup gateway?
- How to verify if this feature works.
I have set up a similar scenario, with R6 as the primary gateway, and R4 as
the backup. R1 is a DHCP client. All three belong to VLAN146. R1 correctly
picks up R6 as the default gateway. But I do not know how to verify if R1
picks up R4 as the backup gateway. When R6 dies, it seems that R1 still points
its default gateway to R6 :((
Thanks in advance for your help.
Rack1R6#
ip dhcp pool VLAN146_POOL
network 155.1.146.0 255.255.255.0
default-router 155.1.146.6 155.1.146.4
!
interface FastEthernet0/0.146
description **** connect to VLAN146
encapsulation dot1Q 146
ip address 155.1.146.6 255.255.255.0
! to simulate as DHCP client
Rack1R1#
!
interface FastEthernet0/0
description **** connect to VLAN146
ip address dhcp
no ip routing
Rack1R1#sh ip int fa0/0
FastEthernet0/0 is up, line protocol is up
Internet address is 155.1.146.2/24
Broadcast address is 255.255.255.255
Address determined by DHCP
Rack1R1#sh ip route
Default gateway is 155.1.146.6
Host Gateway Last Use Total Uses Interface
ICMP redirect cache is empty
Rack1R1#sh arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 155.1.146.1 - 000b.5f76.7280 ARPA FastEthernet0/0
Rack1R1#ping 155.1.146.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.146.6, timeout is 2 seconds:
...
Success rate is 0 percent (0/3)
Rack1R1#sh arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 155.1.146.1 - 000b.5f76.7280 ARPA FastEthernet0/0
Internet 155.1.146.6 0 Incomplete ARPA
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