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DHCP Server on Multiple VLANs [7:49403] posted 07/22/2002
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Hey guys,

     I have a Cisco 3620 connected to a 2948G-L3 which
in turn provides layer three services to a cluster of
3548XLs. I have 9 operating VLANs and have been trying
to work out a scenario for DHCP in my environment.
Right now, we assign static IPs in all 9 vlans because
we do not want to provide seperate DHCP servers for
each. If we could find a way to get one server to
provide DHCP to all the VLANs then we could implement
it. The trick is, each VLAN is a different subnet. 

     I had heard that if you use the 3620 as a DHCP
server, create subinterfaces on a FE port using ISL and
assign IP addresses appropriately, and create multiple
DHCP pools, then the router would issues IPs from pools
that matched the interface it drew the request from.
However, when I try this it just issues IPs from the
first pool until it is full and then moves to the next. 

     Is there a way to make sure the router assigns
correct IPs on the correct sub-interfaces? Is there a
3rd party DHCP server that would do this better?

     Let me do a sample config to show what I tried.
Each network has a network printer at .200 (don't ask)
and a router sub-interface at .1 except the 10.10.10.0
network which has reserved IPs through 100, but still a
router interface at .1

Here's the Cisco 3620 DHCP portion of the config:
!
ip dhcp excluded-address 10.10.10.1 10.10.10.100
ip dhcp excluded-address 192.168.1.1
ip dhcp excluded-address 192.168.1.200
ip dhcp excluded-address 192.168.2.1
ip dhcp excluded-address 192.168.2.200
ip dhcp excluded-address 192.168.3.1
ip dhcp excluded-address 192.168.3.200
ip dhcp excluded-address 192.168.4.1
ip dhcp excluded-address 192.168.4.200
ip dhcp excluded-address 192.168.5.1
ip dhcp excluded-address 192.168.5.200
ip dhcp excluded-address 192.168.6.1
ip dhcp excluded-address 192.168.6.200
ip dhcp excluded-address 192.168.7.1
ip dhcp excluded-address 192.168.7.200
ip dhcp excluded-address 192.168.8.1
ip dhcp excluded-address 192.168.8.200
!
ip dhcp pool Vlan1
  network 10.10.10.0 /24
  dns-server 4.2.2.1
  default-router 10.10.10.1
!
ip dhcp pool Vlan10
  network 192.168.1.0 /24
  dns-server 4.2.2.1 
  default-router 192.168.1.1
!
ip dhcp pool Vlan20
  network 192.168.2.0 /24
  dns-server 4.2.2.1
  default-router 192.168.2.1
!
ip dhcp pool Vlan30
  network 192.168.3.0 /24
  dns-server 4.2.2.1
  default-router 192.168.3.1
!
ip dhcp pool Vlan40
  network 192.168.4.0 /24
  dns-server 4.2.2.1 
  default-router 192.168.4.1
!
ip dhcp pool Vlan50
  network 192.168.5.0 /24
  dns-server 4.2.2.1 
  default-router 192.168.5.1
!
ip dhcp pool Vlan60
  network 192.168.6.0 /24
  dns-server 4.2.2.1 
  default-router 192.168.6.1
!
ip dhcp pool Vlan70
  network 192.168.7.0 /24
  dns-server 4.2.2.1 
  default-router 192.168.7.1
!
ip dhcp pool Vlan80
  network 192.168.8.0 /24
  dns-server 4.2.2.1 
  default-router 192.168.8.1
!
interface FastEthernet1/0
 description connected to Private Network
 no ip address
 duplex auto
 speed auto
!
interface FastEthernet1/0.1
 encapsulation isl 1
 ip address 10.10.10.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.10
 encapsulation isl 10
 ip address 192.168.1.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.20
 encapsulation isl 20
 ip address 192.168.2.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.30
 encapsulation isl 30
 ip address 192.168.3.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.40
 encapsulation isl 40
 ip address 192.168.4.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.50
 encapsulation isl 50
 ip address 192.168.5.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.60
 encapsulation isl 60
 ip address 192.168.6.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.70
 encapsulation isl 70
 ip address 192.168.7.1 255.255.255.0
 no ip redirects
!
interface FastEthernet1/0.80
 encapsulation isl 80
 ip address 192.168.8.1 255.255.255.0
 no ip redirects
!


Thanks,

Don Pezet
dpezet@xxxxxxxxxxxx




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