From: Wilson Chan (wilson@wilsonch.gotdns.com)
Date: Fri Aug 22 2008 - 00:15:32 ART
Thanks Huan for the explanation! I had a feeling that "ip route 0.0.0.0
0.0.0.0 FastEthernet0/0" would arp for all IP's thats were not in the
route table where as the option with "dhcp" would take the gateway IP and
forward the packets to the ISP. :)
-Wilson
>
> Hi Wilson
>
> The second one (with dhcp keyword) is a better option. It will tie the
> default route with a next-hop IP of the gateway.
>
> Have a close look at the difference btw the two static route when you do
> "show ip route static"
>
> R2#sh run | in ip route
> ip route 0.0.0.0 0.0.0.0 FastEthernet0/0
>
> R2#sh ip route static
> S* 0.0.0.0/0 is directly connected, FastEthernet0/0
>
>
>
> R2#sh run | in ip route
> ip route 0.0.0.0 0.0.0.0 FastEthernet0/0 dhcp
>
> R2#sh ip route static
> S* 0.0.0.0/0 [1/0] via 10.1.1.1, FastEthernet0/0
>
>
> Having a default route pointing to a multipoint interface (e.g.
> fastehternet) without the next hop IP, your router will be overwhelm
> with lot of ARP entries (if proxy ARP is enabled on the ISP DHCP
> router). Basically, for every Internet destination IP, your router will
> need to ARP for MAC address. The DHCP server will respond with an arp
> entry for that IP with its own MAC address. Your router will maintain
> all ARP entries for every IP on the Internet that your users try to
> reach. I do not think you want your routers to have potentially a
> million entry ARPcache table!
>
> Regards,
>
> Huan
>
>
> On Thu, Aug 21, 2008 at 9:11 PM, Wilson Chan
> <wilson@wilsonch.gotdns.com>wrote:
>
>> I stumbled upon the "dhcp" option in setting a default route. Is there
>
>> a difference between the two route statements in the example below and
>
>> if there is which is the preferred way and why? Thanks!
>>
>>
>> interface FastEthernet0
>> description ***To ISP***
>> ip address dhcp
>>
>> ip route 0.0.0.0 0.0.0.0 FastEthernet0 ip route 0.0.0.0 0.0.0.0
>> FastEthernet0 dhcp
>>
>>
>>
>> Wilson
>>
>>
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>
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