GroupStudy.com GroupStudy.com - A virtual community of network engineers
 Home  BookStore  StudyNotes  Links  Archives  StudyRooms  HelpWanted  Discounts  Login
RE: IOS DHCP server - how to test assigned backup default gateway? posted 11/10/2008
[Chronological Index] [Thread Index] [Top] [Date Prev][Date Next] [Thread Prev][Thread Next]


Microsoft has a feature Dead Gateway Detection
http://technet.microsoft.com/en-us/library/bb878104.aspx

In term of network design, I would suggest provide a couple of downstream
devices to do HSRP/VRRP/GLBP and hand out the virtual address.

Luan Nguyen
Chesapeake NetCraftsmen, LLC.
www.NetCraftsmen.net



-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of Huan
Pham
Sent: Monday, November 10, 2008 7:48 AM
To: CCIE Lab
Subject: IOS DHCP server - how to test assigned backup default gateway?

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


Blogs and organic groups at http://www.ccie.net

_______________________________________________________________________
Subscription information may be found at: 
http://www.groupstudy.com/list/CCIELab.html