Extended ping facilities

kpjungle

Hi,

Anyone actually 100% into the use of extended pings, in the way of the strict and loose source routing?
As far as I can see, its using a function in the IP header, to determine which path to take. I only found a single useful link on it so far, but im quite interested in it. Its hard to lab something out thats only been sparsely mentioned in texts.

Using the Extended ping and Extended traceroute Commands - Cisco Systems

Let me know if theres more material on it, or if anyone at all actually uses it in any way...

PStefanov

Strict and loose source routing use the the options field in the IP Header. With strict source routing, the sender describes the exact path that a packet should take. However, with loose source routing, it lists only the ip address that the packet should traverse.

Look at the RFC for IPv4: RFC 791 (rfc791) - Internet Protocol and search for "loose source" and "strict source".

HTH,
Pavel

kpjungle

PStefanov wrote: »

Strict and loose source routing use the the options field in the IP Header. With strict source routing, the sender describes the exact path that a packet should take. However, with loose source routing, it lists only the ip address that the packet should traverse. These are generally used with RSVP for MPLS Traffic Engineering.

Look at the RFC for IPv4: RFC 791 (rfc791) - Internet Protocol and search for "loose source" and "strict source".

HTH,
Pavel

Thanks!

Just seemed very obscure to me when i tried to lab it out. Should the list contain the next hop of the next routers incomming interface/vs outgoing interface.. A bit weird..

PStefanov

Just edited the post. Please disregard what I said about the use of these options with RSVP. RSVP actually has an object that does a similar function, but it's within the protocol itself and can specify either an exact route or hops that the reservation should traverse.

With loose routing, you can specify either the ip address of an incoming or outgoing interface. It doesn't really matter as long as you have one path to the destination.

With strict routing, you should specify the exact path and all the ip addresses of incoming interfaces to the destination.

gojericho0

From what I understand, strict requires certain hops to be used and does not allow the use of alternative hops. Loose I believe that certain hops are supposed to used, but if an alternative path is available it can route using this path

kpjungle

PStefanov wrote: »

Just edited the post. Please disregard what I said about the use of these options with RSVP. RSVP actually has an object that does a similar function, but it's within the protocol itself and can specify either an exact route or hops that the reservation should traverse.

With loose routing, you can specify either the ip address of an incoming or outgoing interface. It doesn't really matter as long as you have one path to the destination.

With strict routing, you should specify the exact path and all the ip addresses of incoming interfaces to the destination.

I was looking over the RFC, but I cant tell if it is mandatory for the individual gateways/hosts to respect the list you instill into the header. For example, if i tell a router i want it to use this path to goto a certain destination, is it required to do so? My immediate answer would be a strong No! since that would allow some undesired paths for some networks. Ie service providers with certain policies in place for routing traffic in a certain way.

PStefanov

gojericho0 wrote: »

From what I understand, strict requires certain hops to be used and does not allow the use of alternative hops. Loose I believe that certain hops are supposed to used, but if an alternative path is available it can route using this path

Actually you have to describe the entire path with strict source routing.

Try this scenario

R1-R2-R3-loopback. If you ping the loopback of R3 from R1 with a strict source routing option and specify only R2's incoming interface ip address, you will receive a source route failed unreachable from R2.

PStefanov

kpjungle wrote: »

I was looking over the RFC, but I cant tell if it is mandatory for the individual gateways/hosts to respect the list you instill into the header. For example, if i tell a router i want it to use this path to goto a certain destination, is it required to do so? My immediate answer would be a strong No! since that would allow some undesired paths for some networks. Ie service providers with certain policies in place for routing traffic in a certain way.

By default, Cisco IOS repsects packets with a source route option. You can disable this behaviour and start dropping these packets with the no ip source-route global config command or no ip options drop (this command forces the router to drop all packets with ip options in it).

kpjungle

PStefanov wrote: »

Actually you have to describe the entire path with strict source routing.

Try this scenario

R1-R2-R3-loopback. If you ping the loopback of R3 from R1 with a strict source routing option and specify only R2's incoming interface ip address, you will receive a source route failed unreachable from R2.

Yeah. Everything except the last hop (destination) needs to be specified.

PStefanov

Yes, as I mentioned above, only the incoming interfaces along the path.