Re: DHCP - Failover Configuration (Multiple VLAN/interfaces)

Hi Arthur,

The problem is the EdgeRouters do not have an interface each in VLAN that requires DHCP, they only have an interface in a single VLAN that is used in the local network (the rest are the outside interfaces). My switches handle the routing internally for performance reasons (lots of people copying large files around between VLAN's).

As an example, you cannot configure multiple subnets to failover to the same IP address with this config:

Router 1:

[edit]
admin@er1# show service dhcp-server
 disabled false
 hostfile-update disable
 shared-network-name VLAN100 {
     authoritative disable
     subnet 192.168.1.0/24 {
         default-router 192.168.1.251
         dns-server 10.254.1.10
         dns-server 10.254.1.11
         failover {
             local-address 192.168.45.129
             name VL100
             peer-address 192.168.45.130
             status primary
         }
         lease 86400
         start 192.168.1.1 {
             stop 192.168.1.200
         }
     }
 }
 shared-network-name VLAN500 {
     authoritative disable
     subnet 192.168.5.0/24 {
         default-router 192.168.5.251
         dns-server 10.254.1.10
         dns-server 10.254.1.11
         failover {
             local-address 192.168.45.129
             name VL500
             peer-address 192.168.45.130
             status primary
         }
         lease 86400
         start 192.168.5.1 {
             stop 192.168.5.200
         }
     }
 }

 Router 2:

[edit]
admin@er2# show service dhcp-server
 disabled false
 hostfile-update disable
 shared-network-name VLAN100 {
     authoritative disable
     subnet 192.168.1.0/24 {
         default-router 192.168.1.251
         dns-server 10.254.1.10
         dns-server 10.254.1.11
         failover {
             local-address 192.168.45.130
             name VL100
             peer-address 192.168.45.129
             status secondary
         }
         lease 86400
         start 192.168.1.1 {
             stop 192.168.1.200
         }
     }
 }
 shared-network-name VLAN500 {
     authoritative disable
     subnet 192.168.5.0/24 {
         default-router 192.168.5.251
         dns-server 10.254.1.10
         dns-server 10.254.1.11
         failover {
             local-address 192.168.45.130
             name VL500
             peer-address 192.168.45.129
             status secondary
         }
         lease 86400
         start 192.168.5.1 {
             stop 192.168.5.200
         }
     }
 }
 use-dnsmasq disable

This configuration will result in the following errors over and over again, the relationship between the two peers does not get setup correctly:

Sep  9 07:48:31 er1 dhcpd: Failover CONNECTACK from VL500: remote failover relationship name VL100 does not match
Sep  9 07:48:36 er2 dhcpd: Failover DISCONNECT from VL100: Connection rejected, invalid failover partner.

If you try to set the failover names the same you will get this instead:

admin@er1# commit
[ service dhcp-server ]
Failover names should be unique: 'VL100' has already been configured
DHCP server configuration commit aborted due to error(s).

What I imagine should be possible in the configuration is setting a failover peer up in the global config, then assigning that peer subnet. As an example it would look like this:

 disabled false
 hostfile-update disable
 failover DHCP-Failover {
     local-address 192.168.45.129
     peer-address 192.168.45.130
     status primary
 }
 shared-network-name VLAN100 {
     authoritative disable
     subnet 192.168.1.0/24 {
         default-router 192.168.1.251
         dns-server 10.254.1.10
         dns-server 10.254.1.11
         failover {
             name DHCP-Failover
         }
         lease 86400
         start 192.168.1.1 {
             stop 192.168.1.200
         }
     }
 }
 shared-network-name VLAN500 {
     authoritative disable
     subnet 192.168.5.0/24 {
         default-router 192.168.5.251
         dns-server 10.254.1.10
         dns-server 10.254.1.11
         failover {
             name DHCP-Failover
         }
         lease 86400
         start 192.168.5.1 {
             stop 192.168.5.200
         }
     }
 }
 use-dnsmasq disable

That way the fail over peer is only declared once for each pair of routers, multiple subnets can be assigned the same failover peers that way.

As a work around I can just edit the dhcp config file and restart the service to make it work, but every time someone else makes a change my changes obviously get removed.