From: Victor Cappuccio (cvictor@protokolgroup.com)
Date: Sun Jul 23 2006 - 16:00:01 ART
Hi Sami,
Please allow me on this one:
DHCP is a Service for passing configuration information to hosts on a TCP IP
network as far as I know, and yes you can set 2 Default Gateways via DHCP,
but you will need to method at the client like Gateway Discovery Protocol to
avoid sending packets to a Dead GW
Something similar as this:
ip dhcp excluded-address 170.17.162.2
ip dhcp excluded-address 170.17.162.1
!
ip dhcp pool MYPOOL
network 170.17.162.0 255.255.255.0
default-router 170.17.162.1 170.17.162.2
If we add one host in that network, to see the information provided by this
great live saver feature.
Dummy_Host#show ip route | b Gate
Gateway of last resort is 170.17.162.1 to network 0.0.0.0
170.17.0.0/24 is subnetted, 1 subnets
C 170.17.162.0 is directly connected, Vlan666
S* 0.0.0.0/0 [254/0] via 170.17.162.1
Lets test this,
Dummy_Host#ping 204.12.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 204.12.1.4, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 140/141/144 ms
Yeah seems to work
Now let's shut down the Primary Default Gateway to see what happens
R1(config)#int f0/0
R1(config-subif)#sh
R1(config-subif)#
The information from the Routing Table at Dummy host is not erased
Dummy_Host#show ip route | be Gate
Gateway of last resort is 170.17.162.1 to network 0.0.0.0
170.17.0.0/24 is subnetted, 1 subnets
C 170.17.162.0 is directly connected, Vlan666
S* 0.0.0.0/0 [254/0] via
Let's ping the Def-gw?
Dummy_Host#ping 170.17.162.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 170.17.162.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
does not work :(
So we need a method of getting redundancy with out needing to shut down the
Interface and renewing the IP Address / Default Gw for providing the needed
redundancy.
At R1 and R2 (or the gateways) interface sitting with the dummy host put
this
vrrp 1 ip 170.17.162.1
wit only 1 default-router 170.17.162.1 at the ip dhcp pool MYPOOL, because
it's not logic to gave the 2 if you run some other redundancy method used in
your wording.
And that's it
Dummy_Host#ping 170.17.162.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 170.17.162.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/4 ms
Dummy_Host#ping 204.12.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 204.12.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 112/114/116 ms
Useful debug commands
show arp
show vrrp
show ip int
show ip route
show ip dhcp bind
clear arp
deb arp
ping (always useful)
are great tools in this scenario.
Try it with a couple of routers it would be fun!!
HTH
Victor.-
-----Mensaje original-----
De: nobody@groupstudy.com [mailto:nobody@groupstudy.com] En nombre de Sami
Enviado el: Domingo, 23 de Julio de 2006 06:26 a.m.
Para: ccielab@groupstudy.com
Asunto: DHCP
Group,
Is it possible to provide two default gateway to clients using DHCP ? one
of the task say provide gateway redendency to DHCP clients but don't use
HSRP to achieve this...
Thanks
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