cisco 837 ip issues

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

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Hi Bob,

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

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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 to you, but the link with the ISP uses on your side and on their side, and you then assign the 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 to you, but it does that over with the ISP taking and you taking for your end of the link. You then do whatever you want internally with, 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.)

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Walter Roberson

randalf schrieb:

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.

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