Normal traceroute vs extended traceroute

[Jelani_DTE_PRO]

Yesterday, I tried using normal traceroute to see my hops to Google DNS. Every time I issued that command on my router, it would fail before hitting the internet. Even when I tried an extended traceroute, without a source, it would fail before getting out onto the internet. I was told to use an extended traceroute and source the IP address of that router's LAN... That allowed a successful traceroute to Google DNS, displaying all of the hops used to get there.

What would cause an extended traceroute or ping, require a specific source address range and/or VLAN to give accurate communication information?

Thanks,

Jelani

[Jon Marshall]

It just means that there was a route back to the IP you used as the source for the traceroute whereas without that it used the IP of the exit interface for which there was no route back. 

That is a bit unusual if this is an internet connected router but I have see that behaviour in MPLS networks where the CE to PE subnet is not necessarily advertised between sites. 

Jon 

[Jelani_DTE_PRO]

Hi, Jon.

Actually, the next hop from the last (MPLS) router displayed, should have been the gateway of another internal (Internet) router. From that Internet router, the next hop should been via its public facing interface. And, then a list of ISP routers should have displayed. 

MPLS Hub Router -> LAN GW on Internal Internet Router -> Public Facing Interface on Internal Internet Router -> ISP Routers... -> Google DNS.

[Jon Marshall]

If it is MPLS then you may just be advertising the LAN network to the rest of the network. 

Difficult to say but it does sound like the behaviour I have seen before. 

Jon

[Jelani_DTE_PRO]

So, Jon, you're saying that other devices aren't aware how to get to the PE's equipment for internet connectivity in an MPLS network?

[Jon Marshall]

It's difficult to tell without seeing routing tables etc. 

What I am saying though is that with MPLS you don't necessarily need to advertise the CE to PE link in which case if you ping from the CE there might not be a route back. 

But of course you would need to advertise the LAN behind the CE so there should always be routes back. 

Whether that is your problem like I say it is diffcult to say. 

Jon

[Jelani_DTE_PRO]

What's appropriate to post, when it comes to workplace network device configs?

Curious...

[Jon Marshall]

It's up to you and your company policy really. 

Obviously you would need to remove any sensitive information and the configurations contain public IPs then best to replace some of the octets with "x" or something similar,  our just use private IPs and make it clear what you have done. 

Jon

[Georg Pauwen]

Hello,

can you post the config of your router ? We might spot something unusual...normally, traceroute and ping use the outgoing interface by default, and hence, should succeed...

[Jelani_DTE_PRO]

Hi, Georg.

Anything, in particular?

[Jelani_DTE_PRO]

Thanks, Jon. Appreciate your feedback.