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TOPIC: Routing

Routing 8 years 9 months ago #25142

  • waynocook
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I couldn't find a place where this fit, so, I'm tentatively going to enter it here.

At our facility, we have two subnets, one our business subnet and one for engineering/video.

Business subnet 172.19.2.0/22
Engineering subnet 172.19.20.0/23

On the business subnet, IT installed a host (172.19.2.13) with subnet 255.255.255.255 and no default gateway, on what they termed as a VLAN endpoint....

From the rest of their subnet, they have no problems reaching that host.

From the engineering subnet, however, I cannot ping that host (obviously). In the static routes added on that host, however, they are telling me that the static route will override the absence of the default gateway and answer the server in the engineering subnet and it's application. The server in our network does have the proper setup on its NIC, so there's never been an any issue with it...but the vlan endpoint on the business side sometimes will answer and sometimes not.

I can find very little on the internet about giving a host a /32 netmask and being able to communicate with it across a router on another subnet.
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Re: Routing 8 years 9 months ago #25143

  • Smurf
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I must admit, i have never come across this before myself. I am also intrigued now. Hopefully someone can post an answer to this.

Did you say that some hosts on the Engineering can ping that host ?
Wayne Murphy
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Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit www.sec-1.com or PM me for details.
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Re: Routing 7 years 9 months ago #29298

  • NeoTech
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im only a student but i'll have a pop at this one...

provided the network is set up correctly for routing between vlans. im willing to bet your problem is due to network traffic flow. If there is a lot of congestion on the new hosts side, there will be a lot of collisions, late replies etc and the network communication between the 2 machines will simply time out. Other times it may get through if there happens to be less traffic at that given moment.

Now the new host has a broadcast subnet mask (255.255.255.255) and with the 2 departments being on different subnets, i believe the intention may be to broadcast information, (perhaps a video feed or similar?) to the whole business subnet only but the network topology may not be equipped to handle it as this could generate a lot of network traffic if this is the case. The vlan end point may need to be attached to a switch that has enough memory to handle a lot of broadcasts, aswell as the incomming and outgoing traffic for the other machines attached to it. If the switch cannot handle it all it may well randomly drop packets.
A good solution here, if not already implimented would be to create redundant loops by adding a few more switched to the topology on the vlan end point's end and have any other machines attached to the switch connect to the new switches. Configure spanning tree protocol correctly and you will have minimised traffic flow to and from the broadcast machine as the switches will choose easier paths for each machines traffic.

Now i may be in over my head here but, Smurf if you're reading and care to respond, would the vlan end machine which has a broadcast subnet mask also not need a broadcast host ip ie.172.19.2.255 instead of 172.19.2.13??? And may i have an explaination of why i have just confused myself with that last bit? lol.

Neo
Tech
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Re: Routing 7 years 9 months ago #29301

  • NeoTech
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Ah i am way wrong... I couldnt stop thinking about the problem and decided to do a bit of research.
it is actually for configuring loopback addresses on the machine so a loopback network address can be advertised to each subnet for communication...
confusing? not really. Think of it as creating virtual ports and giving each one of those a seperate ip address so each vlan can communicate with the host individually. 172.19.2.13 could infact be 1 of 2 IPs configured on the device if this method has been used. The other address may be part of the other network so both subnets can communicate individually with the host. I should have realised that having only passed CCNA 3 a few weeks ago.

see this page for more info i believe it is a similar concept!:

www.petri.co.il/how-30-and-32-bit-IP-sub...cisco-networking.htm

Although it talks about routers, (you didn't state whether the other host was infact a PC or a different device). it may be possible with a workstation???

feedback guys please!

Neo
Tech
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Re: Routing 7 years 9 months ago #29307

  • TheBishop
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Sometimes responds and sometimes doesn't eh? Try adding the (correct) MAC and IP addresses into the hosts files on both machines and also the machine names and IP addresses into the lmhosts files on both machines
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Re: Routing 7 years 9 months ago #29308

  • Smurf
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I am more confused at how you can get hosts on the same network working. With the Subnet Mask, it will determine that its on a different network id and would therefore would think it needs to route the traffic.

Hmmm....
Wayne Murphy
Firewall.cx Team Member
www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit www.sec-1.com or PM me for details.
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