help me understand router ip's

[kaizer]

hello
i don't know routers
what i want to understand is this:
i know our company router (cisco 1700) has an internal ip (192.168.31.1)
it also has another ip which is considered "outside" of 205.158.200.x
i forget the exact ip
there is also a "wan" ip address in the 64.221.x.x range
so, now, what is the significance of the outside vs the wan ip?
i figured there would just be 2 addresses - an inside and an outside
We do have nat if that makes a difference

thanks

 

[schofs]

Ok without seeingyour network this is a could be

1. Inside should be the LAN in your local site

2. Outside could be the Internet

3. WAN could be another site within your company you have a connection toi.e another office

 

[reliancetech]

Well schofs can be correct but I can usederstand this as

1) 192.168.31.1 -- This is IP address of your internal network.

2) 205.158.200.x -- This can be IP of serial interface to connect to other end (WAN )network router.

3) WAN -- Wan is your remote site/office

NAT is address transalater use to reserve/fool IP addresses pool.

 

[kaizer]

hello
thx for your replies
we do not have any other sites
the wan ip is in range 64.x.x.x (don't have the exact ip handy)

 

[lambent]

2 ISPs? One is backup?

 

[tandrews1]

192.186.31.1 is your internal network

205.158.200.x could be a range of addresses your internal addresses are translated to.

64.x.x.x could be the address your isp uses on that interface to route traffic to you.

 

[kaizer]

thanks tandrews1
i think that may be the answer
I know for a fact that our internal ip's are translated to those 205.xx....'s


however, if u don't mind, could you explain what you mean by "64.x.x.x could be the address your isp uses on that interface to route traffic to you"

 

[tandrews1]

Sure...

We use all 10.x.x.x addresses on our internal network. The address on E0 is 10.2.0.x

Our ISP has allocted a small block of globally routable ip addresses on the 209.191.213.x network. I have statements in the router that translate (either statically or dynamically) my internal 10.x addresses to 209.191.213.x addresses.

Our ISP has a fairly complex network setup, and in order to route traffic to and from our network they assign us addresses that are internal to their network...so E1 on our router has a 172.x.x.x address that our ISP allocated to us.

This may explain your 64.x.x.x network. The outside interface on your router may have a 64.x.x.x address so that when traffic is inbound to one of your 192.168.31.x addresses, your ISP sees that address, looks at their routing tables and sends that data to your router at 64.x.x.x, which then has all the routing information to get the data to the correct host on your network.

 

[kaizer]

thank you again tandrews
this is all starting to make sense now
but
1)on the router outside interface, isn't there just one incoming line (the T1)? so i would expect it to have a 205.x address. Or, are you saying that for routing purposes, that interface has a 64.x assigned as well?

Do you mean that the isp routes from their 64.x net to our assigned 205.x and then nat translates to the internal 192.x host?

i know that my routers address is 205.158.x.y which i use as 192.168.31.1 for gateway purposes on pc ip configs

thx much

 

[tandrews1]

Pretty tough to say without actually seeing the router config... everything I typed above is speculation, but I can tell you this...

If you are using 192.168.131.1 as the gateway when setting up TCP/IP on your workstations, then the inside address of your router is 192.168.131.1.

If your internal numbers are being translated to 205.158.x.x addresses there won't neccessarily be a 205.x address on any of your router interfaces... the translations are handled with NAT commands, which requires an inside interface and an outside interface. Your router has a default route set on it, and if I had to make a bet I would bet that the default route is pointing to one of your ISP's routers sitting at 64.something.

 

[kaizer]

thx tandrews
u may make me into a router guy when this is over!
i happen to have an old printout of the router config
there is a
interface serial0
ip address 64.x 255.255.255.252
ip nat outside
etc etc

also
ip address 192.168.31.1 255.255.255.0
ip address 205.158.x 255.255.255.192 secondary

also

ip route 0.0.0.0 0.0.0.0 serial0

does this make it easier for u to explain it to me?
thx

 

[tandrews1]

The config above would certainly correspond with what I was suggesting...

Serial0 does have the 64.x.x.x address and your ISP will have a 64.x.x.x address on the same subnet on one of their router interfaces. The default route is to Serial0, so anything your router can't handle gets pushed out that interface.

You snipped a bit too much from the config, but I'm guessing that you have an "interface ethernet0" statement before the "ip address 192.168..." lines. Does the config contain statements that begin with "ip nat ... "? That would tell you what your internal addresses are getting translated to. Looking at your config, I doubt that they are getting translated to 205.158.x.x addresses, because that subnet is tied to your inside ethernet interface (the "ip address 205.158.x 255.255.255.192 secondary" statement), which generally means you have hosts on the network that have ip addresses on that subnet already (otherwise you wouldn't be translating)

 

[kaizer]

there is the following:
ip nat inside source list 1 interface serial0 overload
and
ip nat inside source static 192.168.31.100 205.158.x.x (address of email server)

i do think our mappings go to the 205's

but what do u make of it???

 

[tandrews1]

If every host inside the network has an address on the 192.168.x.x network, then there is no need for the secondary address (205.158.x.x) on the inside interface. That is precisely what network address translation does for you... a packet comes in bound for your mail server (let's pretend it's globally routable address is 205.158.1.3)... your router looks at that packet, sees the address and translates it to 192.168.31.100 per the static assignment in the above config.

 

[JOAMON]

You should change the default route to the next hop ip...
If serial0 is for example 64.120.120.6 then set as follows..
ip route 0.0.0.0 0.0.0.0 64.120.120.5

Always use numbered address for default route whenever possible. When set to an interface it will arp every address going to the internet and the arp table will become huge where when set to ip address arp will only have table of lan and wan ip blockes.