4

Would one ever find a router that had been intentionally configured to not have any default routes? No default gateway, no 0.0.0.0/0...

Sort of an academic question, someone at work mentioned it, and it seems a bit crazy to me. Even large backbone routers would need to have a default route if they had an address they didn't recognize...

I don't know much about BGP, so I may be shooting myself in the foot here.

5

As Ron Maupin pointed out, this is not uncommon. It's especially used between autonomous systems speaking BGP, and there actually is a thing called the "Default Free Zone", the core of the internet in which no default gateways are configured: all routes are exchanged via BGP.

Not having default routes there actually serves a purpose: it prevents traffic to unallocated destinations to be discarded at the first possible hop, so it will not bounce between networks.

2

This is certainly something that is done. If your WAN routers have full Internet routing tables, then, at least in theory, your WAN routers know how to reach every public address on the public Internet. A default route would only allow routers configured this way to send traffic with a a destination not in the routing table to the ISP routers, but the WAN routers should have the same routing knowledge as the ISP routers.

2
  • Ok! I figured it was something along those lines, but it almost seems impossible for a WAN router to know every possible route. Like I said, I barely understand BGP and that's probably where this magic comes from. Thanks for the info!
    – Shrout1
    Mar 10 '17 at 4:15
  • You need to understand the size and speed of these type of routers. There are well over 600,000 IPv4 routes in the full Internet routing table. Take for example an ISP with multiple connections to multiple other ISPs. That ISP certainly doesn't want a default route to any one of the other ISPs, it wants the traffic to take the shortest path. Large companies with multiple ISP connections are the same way.
    – Ron Maupin
    Mar 10 '17 at 4:18
2

Having default route 0.0.0.0/0 Configured in router totally depend upon taffic flow . If there is no internet traffic in setup . Then there is no need of default route Configuration in routers . Because when user is browsing resouces from internet packet will take default route in router pointing to gateway of ISP

Router(config)# ip route 0.0.0.0 0.0.0.0 pointing towards gateway of ISP

In network if users are not having requirement of browsing internet resources then no need of default route Configuration . Only specific routes is enough for connecting different private networks

1
  • That is a fair point; certainly an internal network that is separated from the internet could function solely on static routes. I have managed networks like this in the past myself. My question was in relation to the broader internet, but you make a good point!
    – Shrout1
    Jan 5 at 18:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.