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illuminatus
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Routing Worked then Stopped

Thu May 12, 2005 9:08 pm

I was wondering if you could shed some light on this. I don't know if you have experience with Mikrotik, but I know you have experience with routers in general. Last night I was setting up a Mikrotik box with the following setup:

Image

Have to use the 3com router in between because plugging in the modem directly into the Mikrotik does not establish a link for some reason.

The Mikrotik also runs 3 more networks with 10.59.1.0/24, 176.16.0.0/16, and 192.168.1.0/24 networks. All 3 networks had DHCP servers enabled on their interfaces. I had it setup so all the networks used 192.168.254.1 as their default gateway and they could see eachother via source and destination NATs. I also setup some bandwidth throttling and a little bit of QoS. Seemingly, I had everything working.

When I plugged into each network interface using a laptop and a straight through cable and everything seemd to work. I could ping outside and do DNS queries as well as browse the web, etc. when I plugged into every interface. After some cable management was done, however, and the Mikrotik was hooked back up I could no longer ping 192.168.254.1. Consequentially I couldn't get to anywhere on the net.

If you knew anything that could cause this or maybe just give some helpful helpful insight on this situation.
 
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andrewluck
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Thu May 12, 2005 10:20 pm

The default gateway on each network has to be an IP address on that network. So, for example, on 192.168.1.0/24 the gw should be 192.168.1.1. The MT router should have a default gateway of 192.168.254.1.

Regards

Andrew
 
mp3turbo2
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Fri May 13, 2005 12:44 pm

> The default gateway on each network has to be an IP address on that network.

you'd be suprised but it doesn't have to be.
 
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andrewluck
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Fri May 13, 2005 4:24 pm

Yes, I'm surprised. Without using proxy-arp?

The gateway is the next hop address. The client has to be able to reach it with a layer 2 broadcast in order to determine where to send the ethernet frame.

Explain.

Regards

Andrew
 
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tneumann
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Fri May 13, 2005 6:30 pm

Yes, I'm surprised. Without using proxy-arp?
Yes.
The gateway is the next hop address. The client has to be able to reach it with a layer 2 broadcast in order to determine where to send the ethernet frame.
That's correct (for non point-to-point links, anyway) but some
routing platforms have a mechanism
called "recursive route lookup", whereby direct Layer-2 reachability
of the next-hop may be deduced in multiple steps by recursively
looking up gateways until one with direct Layer-2 reachability
is indeed found.

According to

http://www.mikrotik.com/download/CHANGELOG_beta
What's new in v2.9beta1:

*) routes now support recursive nexthop lookup;
So this works starting with 2.9

--Tom
 
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andrewluck
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Fri May 13, 2005 6:47 pm

Tom

Thanks for the explanation. Looks like I'm behind the curve again. Time for some more reading :shock:

Regards

Andrew

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