I currently have my default route set to be ip route 0.0.0.0 0.0.0.0 FastEthernet0/0 on my 2611XM. The problem with this is that it causes the ARP table to be huge as it sends requests out for every single connection through the router. This results in the first packet being dropped for new IP addresses and causes a noticeable delay when browsing web pages upon the first connection. Needless to say, this is very annoying. I know one way to fix this is to assign the next hop an IP address as opposed to an interface. The problem here is that my IP address through my ISP is DHCP assigned. Is there a way to resolve this issue without having the next hop as an IP address or asking the ISP to provide me a static address?
You have correctly identified several of the issues when you point a static route (and most especially a static default route) at an Ethernet interface. In addition to the size of the ARP table and the dropped packets while the router sends the ARP request there are several other potential problems:
- this depends on the next hop supporting proxy arp. If the next hop device does not support proxy arp then your static route will not work - and in my experience increasingly network administrators are disabling proxy arp due to security concerns.
- in addition to the memory used by the very large ARP table it will increase CPU utilization - remember that every entry in the ARP table is flushed and re-learned every 4 hours. So the router CPU is removing entries, sending an ARP request, receiving an ARP response, and building a new entry in the ARP table.
Depending on the version of software that you are running, there should be an option in configuring yout static route to specify DHCP where you would normally put the next hop address.
It is not usually true that you get a different IP address every time that the lease expires. Especially when the interface remains up, when the lease expires the client will usually negotiate to obtain the same IP address, and usually does get the same address assigned.
It is certainly true that sometimes you will get a different IP address when using DHCP and that could impact the routing logic. But for using it on a router it would normally not be every time that the lease expires.