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Is ARP entry required when a floating static route is configured?

jngamp
Level 1
Level 1

Perhaps this is only the case in Packet Tracer and doesn't happen with real devices. 
But I was building a simple setup in packet tracer to test static routes and came across something that confuses me. 

Here's a screenshot of what I set up:

jngamp_0-1674815394907.png

I set static routes on the first two routers (from left to right) towards the subnets on their right. 

On the router on the right I set a floating static route 0.0.0.0 0.0.0.0 with exit interface g0/0/0.

I then initiated traceroute on the left PC with the right PC as target. When TTL was set to 3 the ICMP request reached the router on the right, which decreased TTL to zero, dropped the packet and created a ICMP type 11 message (time exceeded) and packaged it in an IP packet with destination address of the left PC.

Here's what confuses me: I thought that with the floating static route set, the package will simply be sent out via g0/0/0 (although I didn't think through what MAC address would be used). But instead an ARP request was sent out for the destination address.

I don't see why the ARP table was consulted for the destination address if a floating static route was set. Did I miss something?

1 Accepted Solution

Accepted Solutions

Seb Rupik
VIP Alumni
VIP Alumni

Hi there,

You will find that the router will ARP for every destination address leaving via Gi0/0/0 since you have not specified a

 next-hop

gateway address. You can get around this by changing the link between the routers to a

point-to-point

link.

I wrote a blog post about this behaviour:

Static route next-hop – CS7 Networks

 

cheers,

Seb.

View solution in original post

2 Replies 2

Seb Rupik
VIP Alumni
VIP Alumni

Hi there,

You will find that the router will ARP for every destination address leaving via Gi0/0/0 since you have not specified a

 next-hop

gateway address. You can get around this by changing the link between the routers to a

point-to-point

link.

I wrote a blog post about this behaviour:

Static route next-hop – CS7 Networks

 

cheers,

Seb.

jngamp
Level 1
Level 1

Thank you. I mixed up the terminology also, I set up a default route and not a floating static route. 

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