A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this. Ralph Doncaster principal, IStop.com On Sun, 6 Oct 2002, Stephen J. Wilcox wrote:
I dont understand this..
A wants to get to a network which it [thinks it] is not connected to, the only route is via B. therefore you must advertise the route from B with next hop B
the only possible way (at least in ethernet IP) that A can send direct onto the ethernet segment is if it is connected to the other (172.16) network and if youre not willing to do that then your solution is not possible
Steve
On Sun, 6 Oct 2002, Ralph Doncaster wrote:
Background: Router A and B are connected via a common ethernet segment 1. Router A uses 10.10.10.1/30, and Router B uses 10.10.10.2/30. Router B also has another subnet configured for ethernet segment 1; 172.16.16.0/24.
When I setup a situation like the above, with Router B advertising the 172.16.16.0/24 to router A, router A sees a next hop of 10.10.10.2. This is not good since packets from A going to the 172.16.16 subnet get sent to Router B, which then ARPs the desitnation, instead of just being ARPed by router A.
I don't want to turn on ICMP redirects on B since they're insecure and ugly. I've also made sure I'm not using next-hop self. Is there a way to make this work?
Ralph Doncaster principal, IStop.com
On Sun, Oct 06, 2002 at 04:25:00PM -0400, Ralph Doncaster wrote:
A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this.
There are two solutions to your dilemma: - Route via B - Add A to 172.16.16.0/24 It's not a matter of dynamic routing, it's just the way subnets work. If you want all the hosts to be able to talk to each other directly, put them all on the same subnet. That you don't want to accept either solution doesn't mean that there is no solution. "I want to define subnets, but I want hosts on said subnets to ignore their boundaries" does not make sense. -c
On Sun, 6 Oct 2002, Clayton Fiske wrote:
On Sun, Oct 06, 2002 at 04:25:00PM -0400, Ralph Doncaster wrote:
A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this.
There are two solutions to your dilemma:
- Route via B
- Add A to 172.16.16.0/24
It's not a matter of dynamic routing, it's just the way subnets work. If you want all the hosts to be able to talk to each other directly, put them all on the same subnet.
It seems I'm not the only idiot asking these types of questions. I found there's a whole RFC about it. http://www.ietf.org/rfc/rfc1433.txt -Ralph
No its not possible to say you can reach the subnet on the same media... IP maps to the [Ethernet] with ARP, but before a packet is passed down to MAC via ARP it is routed and if there is no route to the connected ethernet then it will necessarily need to use the other router. You must have the route before you can look at passing it to the media.. Steve On Sun, 6 Oct 2002, Ralph Doncaster wrote:
A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this.
Ralph Doncaster principal, IStop.com
On Sun, 6 Oct 2002, Stephen J. Wilcox wrote:
I dont understand this..
A wants to get to a network which it [thinks it] is not connected to, the only route is via B. therefore you must advertise the route from B with next hop B
the only possible way (at least in ethernet IP) that A can send direct onto the ethernet segment is if it is connected to the other (172.16) network and if youre not willing to do that then your solution is not possible
Steve
On Sun, 6 Oct 2002, Ralph Doncaster wrote:
Background: Router A and B are connected via a common ethernet segment 1. Router A uses 10.10.10.1/30, and Router B uses 10.10.10.2/30. Router B also has another subnet configured for ethernet segment 1; 172.16.16.0/24.
When I setup a situation like the above, with Router B advertising the 172.16.16.0/24 to router A, router A sees a next hop of 10.10.10.2. This is not good since packets from A going to the 172.16.16 subnet get sent to Router B, which then ARPs the desitnation, instead of just being ARPed by router A.
I don't want to turn on ICMP redirects on B since they're insecure and ugly. I've also made sure I'm not using next-hop self. Is there a way to make this work?
Ralph Doncaster principal, IStop.com
A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this.
Nope, you need to have IP route for it. If you choose not to tell the second router that it can do it, it would never even try. Repeat after me "My router does not call ms. Cleo to find out what I want. Router follows my instructions to the letter. I forgot to tell my router to do something. It therefore refused to do that something. I shall tell my router to do what I want it to do. It will follow my direct instruction." Now either configure a secondary IP on the second router, or create IP route pointing to the router that knows how to get to the destination. Alex
Please do NOT confuse PHYSICAL plumbing with LOGICAL plumbing. Based on your description, router A and B ARE NOT on the same broadcast domain, with respect to 172.16.16/24. THey are on the same broadcast domain as 10.10.10.0/30 But thats it. In otherwords, No it is NOT technically possible for B to tell A that what it wants is on the same media. Welcome to one of the few down falls of loading up multiple nets on the same physical interface. On Sun, Oct 06, 2002 at 04:25:00PM -0400, Ralph Doncaster wrote:
A and B are connected via the same multi-access media. It is technically possible for B to tell A "you can reach 172.16.16.0/24 on the same media that you receive this update on". However what people seem to be saying is that there is no dynamic routing protocol that implements this.
Ralph Doncaster principal, IStop.com
On Sun, 6 Oct 2002, Stephen J. Wilcox wrote:
I dont understand this..
A wants to get to a network which it [thinks it] is not connected to, the only route is via B. therefore you must advertise the route from B with next hop B
the only possible way (at least in ethernet IP) that A can send direct onto the ethernet segment is if it is connected to the other (172.16) network and if youre not willing to do that then your solution is not possible
Steve
On Sun, 6 Oct 2002, Ralph Doncaster wrote:
Background: Router A and B are connected via a common ethernet segment 1. Router A uses 10.10.10.1/30, and Router B uses 10.10.10.2/30. Router B also has another subnet configured for ethernet segment 1; 172.16.16.0/24.
When I setup a situation like the above, with Router B advertising the 172.16.16.0/24 to router A, router A sees a next hop of 10.10.10.2. This is not good since packets from A going to the 172.16.16 subnet get sent to Router B, which then ARPs the desitnation, instead of just being ARPed by router A.
I don't want to turn on ICMP redirects on B since they're insecure and ugly. I've also made sure I'm not using next-hop self. Is there a way to make this work?
Ralph Doncaster principal, IStop.com
participants (5)
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alex＠yuriev.com -
Clayton Fiske -
John M. Brown -
Ralph Doncaster -
Stephen J. Wilcox