Cisco Systems cisco 837 ip issues

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Subject Author Date
cisco 837 ip issues randalf 01-26-06
Posted by randalf on January 26, 2006, 2:00 pm
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it is possible to assign the static ip address given to me by my adsl isp to
one of the four ethernet interfaces on my cisco 837



cheers for any info



Posted by Peter on January 26, 2006, 7:53 pm
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Hi Bob,

> it is possible to assign the static ip address given to me by my adsl isp to
> one of the four ethernet interfaces on my cisco 837

Dare I ask, but why would anyone want to do this and chuck away 90% of
the capability of the 837?

In theory yes it can be done, but there can be a lot of if's, buts and
"it all depends" in getting it working. Unless you have a real burning
need to do this, I would strongly recommend using the NAT capabilities
of the Router, you lose nothing and gain a heap of other options...

In simple terms, you would need to BRIDGE your WAN data to the
Ethernet, but that almost completely removes the ability to use the
837 to do anything intelligent. The bottom line is that configuring
this depends on quite a bit more technical detail from your ISP about
exactly HOW they are delivering their service to you and exactly what
you want to do with it

Cheers.........pk.

--
Peter from Auckland.

Posted by Walter Roberson on January 26, 2006, 11:20 pm
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>it is possible to assign the static ip address given to me by my adsl isp to
>one of the four ethernet interfaces on my cisco 837

There is some specialized commercial (e.g., hotel) equipment that
the below does not apply to, but other than that:

For a router, any particular IP address range can be either
routed or bridged. If the IP address *range* is routed, then
it can appear on exactly one of the interfaces; if it is bridged,
then the bridged interfaces act as a switch, with a single logical
routing layer applied to the aggregate.

Either way, you cannot have an IP address assigned to one interface,
and a distinct IP address of the same subnet assigned to a different
interface.

You have about three choices:

A) "Don't do that!"

B) subnet the IP address range, and negotiate with the ISP so that
it routes the entire range to you but that the link to the ISP
uses a subnet. For example, ISP routes all of 123.45.67.80/255.255.255.240
to you, but the link with the ISP uses 123.45.67.81/255.255.255.248
on your side and 123.45.67.82/255.255.255.248 on their side, and
you then assign the 123.45.67.88/255.255.255.248 subnet to the second
interface

C) have the ISP route the entire subnet to you, but arrange with
the ISP so that that is layered on top of a distinct /30. For
example, the ISP routes all of 123.45.67.80/255.255.255.240 to you,
but it does that over 111.122.133.144/255.255.255.252 with the ISP
taking 111.122.133.145/255.255.255.252 and you taking
111.122.133.146/255.255.255.252 for your end of the link. You then
do whatever you want internally with 123.45.67.80/255.255.255.240,
subnetting it (perhaps with different sized subnets) over your
various interfaces.


One of the suboptions of A) "Don't do that!" is to use NAT
on your router (or firewall) to accept the additional public IPs
"as is" and to translate them into different internal IP addresses
that might happen to internally be on different interfaces.


If your ADSL ISP operates like my cable ISP, then their offer
to sell you additional static IP addresses is probably mostly
a crock. Hereabouts, on anything less than the "Premium Business
Package", additional static IPs cost $C20 per month -each-
(residential connection itself: $C40/month). The cable ISP here
does not assign a subnet to you and does not route the
static IPs over a carrier IP (such as to your firewall): instead,
the ISP watches for DHCPs from distinct MAC addresses reaching
your cable modem, and does static DHCP mapping for the MACs.

This kind of situation is useless if you are running a router or
firewall: the only thing it works for is if you have a hub
or switch connected to the ISP modem and all of your devices
sit "raw" on the hub/switch and are not even LAN'd together
[unless it be via seperate NICs for that purpose.] You can't
even put in a firewall and proxy-arp for the static IP addresses,
not unless you manage to find a firewall that will bother to
DHCP via distinct MACs for the multiple outside addresses
(which is not something you can do in IOS or PIX.)

Posted by Uli Link on January 28, 2006, 5:51 am
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randalf schrieb:

> it is possible to assign the static ip address given to me by my adsl isp to
> one of the four ethernet interfaces on my cisco 837

With IOS 12.3(8)YG3, 12.3(14)T or 12.4 you have a fully routable
Ethernet2 interface on the physical FastEthernet Port4. DMZ or WAN backup.

The FastEthernet Ports of the 83x series is layer2 only. You cannot
assign IP addresses. You can set a ports speed and duplex settings.

--
Uli


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