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From: John Navas on 1 Jul 2006 12:26
On Sat, 01 Jul 2006 09:33:14 -0400, Robert Coe <bob(a)1776.COM> wrote in
<5nsca2tn9lsnfi6d3b94qt6lrkla4a110p(a)4ax.com>:

>What kept me from seeing the issue clearly from the beginning was that only
>some of the AP's settings got reset. The instructions didn't say that could
>happen, and no Linksys upgrade has done that to me before. I probably would
>have realized what was happening a lot sooner if, as John Navas proposed, the
>AP's own IP address had gotten reset, but it didn't. In fact I believe the AP
>was still querying the DHCP server correctly; it was just ignoring the gateway
>address the DHCP server gave it. Very strange behavior.

Access points (unlike routers) don't query DHCP servers because they
don't care about IP addresses. They are simply bridges that just pass
data link layer traffic back and forth, including DHCP traffic from
clients talking to DHCP servers on the other side of the bridge. The
management interface address of the access point is set manually, not by
DHCP.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_How_To>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>
From: Robert Coe on 1 Jul 2006 12:50
On Sat, 01 Jul 2006 16:26:53 GMT, John Navas <spamfilter0(a)navasgroup.com>
wrote:
: On Sat, 01 Jul 2006 09:33:14 -0400, Robert Coe <bob(a)1776.COM> wrote in
: <5nsca2tn9lsnfi6d3b94qt6lrkla4a110p(a)4ax.com>:
:
: >What kept me from seeing the issue clearly from the beginning was that only
: >some of the AP's settings got reset. The instructions didn't say that could
: >happen, and no Linksys upgrade has done that to me before. I probably would
: >have realized what was happening a lot sooner if, as John Navas proposed, the
: >AP's own IP address had gotten reset, but it didn't. In fact I believe the AP
: >was still querying the DHCP server correctly; it was just ignoring the gateway
: >address the DHCP server gave it. Very strange behavior.
:
: Access points (unlike routers) don't query DHCP servers because they
: don't care about IP addresses. They are simply bridges that just pass
: data link layer traffic back and forth, including DHCP traffic from
: clients talking to DHCP servers on the other side of the bridge. The
: management interface address of the access point is set manually, not by
: DHCP.

That paragraph is, quite simply, bullshit. The most charitable comment I can
manage is that Dr Navas must never have had the opportunity to read the user's
manual of a WAP54G, the type of access point at issue in this discussion.
(BTW, John, it's available on the Linksys Web site.)
From: John Navas on 1 Jul 2006 13:06
On Sat, 01 Jul 2006 12:50:31 -0400, Robert Coe <bob(a)1776.COM> wrote in
<jb9da2lrqp4e196h8biegd4b4sfqls39bg(a)4ax.com>:

>On Sat, 01 Jul 2006 16:26:53 GMT, John Navas <spamfilter0(a)navasgroup.com>
>wrote:
>: On Sat, 01 Jul 2006 09:33:14 -0400, Robert Coe <bob(a)1776.COM> wrote in
>: <5nsca2tn9lsnfi6d3b94qt6lrkla4a110p(a)4ax.com>:
>:
>: >What kept me from seeing the issue clearly from the beginning was that only
>: >some of the AP's settings got reset. The instructions didn't say that could
>: >happen, and no Linksys upgrade has done that to me before. I probably would
>: >have realized what was happening a lot sooner if, as John Navas proposed, the
>: >AP's own IP address had gotten reset, but it didn't. In fact I believe the AP
>: >was still querying the DHCP server correctly; it was just ignoring the gateway
>: >address the DHCP server gave it. Very strange behavior.
>:
>: Access points (unlike routers) don't query DHCP servers because they
>: don't care about IP addresses. They are simply bridges that just pass
>: data link layer traffic back and forth, including DHCP traffic from
>: clients talking to DHCP servers on the other side of the bridge. The
>: management interface address of the access point is set manually, not by
>: DHCP.
>
>That paragraph is, quite simply, bullshit. The most charitable comment I can
>manage is that Dr Navas must never have had the opportunity to read the user's
>manual of a WAP54G, the type of access point at issue in this discussion.
>(BTW, John, it's available on the Linksys Web site.)

I stand corrected -- the WAP54G can have the address of its management
interface set by DHCP. However, that won't necessarily be helpful,
since it won't necessarily be on the same subnet, which is of course the
symptom described by the OP.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_How_To>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>
From: Jeff Liebermann on 1 Jul 2006 13:03
John Navas <spamfilter0(a)navasgroup.com> hath wroth:

>Access points (unlike routers) don't query DHCP servers because they
>don't care about IP addresses. They are simply bridges that just pass
>data link layer traffic back and forth, including DHCP traffic from
>clients talking to DHCP servers on the other side of the bridge. The
>management interface address of the access point is set manually, not by
>DHCP.

I beg to differ. Although the default setting is usually a static IP
address, most access points allow the IP address to be set via DHCP.

For example:

DLink DWL-2100AP:
http://support.dlink.com/emulators/dwl2100ap/html/CfgIpSetup.html

DLink DWL-7100AP:
http://support.dlink.com/emulators/dwl7100ap/html/CfgIpSetup.html

Dlink DWL-900AP+:
http://support.dlink.com/emulators/dwl900ap+_revC/h_lan.html

Sorry, no Linksys examples until www.linksysdata.com/ui/ comes back.
My foggy memory seems to vaguely recall that these also support IP
address setting via DHCP.

The problem is what to do about the gateway IP address. Note that the
default value for the gateway on the above examples is blank or
0.0.0.0 which means no default gateway. That makes sense as you would
not want your return packets going off to the internet when they
should be going to whatever IP is originating the packets. The only
time one needs a real gateway IP is when the access point needs to get
or send something to or from the internet. That can be time sync,
update checks, logging output, and possibly DNS lookups. Otherwise,
no gateway is required or desired.

Another uncommon problem is what to do if the gateway IP address
happens to be outside of the netmask IP address range. This can
happen if the LAN is divided into subnets. All current desktop OS's
support this, but it seems to be lacking in commodity routers and
access points. It's not a big problem but should be consdered for
complex network topologies. (The easy solution is to alias the
internet gateway router with a LAN gateway IP in each sub-net).

--
Jeff Liebermann jeffl(a)comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Robert Coe on 1 Jul 2006 14:13
On Sat, 01 Jul 2006 10:03:18 -0700, Jeff Liebermann
<jeffl(a)comix.santa-cruz.ca.us> wrote:
: John Navas <spamfilter0(a)navasgroup.com> hath wroth:
:
: >Access points (unlike routers) don't query DHCP servers because they
: >don't care about IP addresses. They are simply bridges that just pass
: >data link layer traffic back and forth, including DHCP traffic from
: >clients talking to DHCP servers on the other side of the bridge. The
: >management interface address of the access point is set manually, not by
: >DHCP.
:
: I beg to differ. Although the default setting is usually a static IP
: address, most access points allow the IP address to be set via DHCP.
:
: For example:
:
: DLink DWL-2100AP:
: http://support.dlink.com/emulators/dwl2100ap/html/CfgIpSetup.html
:
: DLink DWL-7100AP:
: http://support.dlink.com/emulators/dwl7100ap/html/CfgIpSetup.html
:
: Dlink DWL-900AP+:
: http://support.dlink.com/emulators/dwl900ap+_revC/h_lan.html
:
: Sorry, no Linksys examples until www.linksysdata.com/ui/ comes back.
: My foggy memory seems to vaguely recall that these also support IP
: address setting via DHCP.

I'm pretty sure that all current Linksys APs, and the WAN side of all their
current routers, support DHCP. I've used several, and they all did.

: The problem is what to do about the gateway IP address. Note that the
: default value for the gateway on the above examples is blank or
: 0.0.0.0 which means no default gateway.

In the WAP54G it's 192.168.1.1 (which, probably not coincidentally, is the
default LAN-side address of most Linksys wireless routers). The default
address of the AP itself is 192.168.1.245, for no obvious reason. Each Linksys
model seems to go with a different randomly chosen number in the fourth octet.

: That makes sense as you would
: not want your return packets going off to the internet when they
: should be going to whatever IP is originating the packets. The only
: time one needs a real gateway IP is when the access point needs to get
: or send something to or from the internet. That can be time sync,
: update checks, logging output, and possibly DNS lookups. Otherwise,
: no gateway is required or desired.

Well, that's assuming you have a flat network. Our network is broken up into
about a dozen subnets, so the probability that a given packet has to go
through the gateway is pretty high.

: Another uncommon problem is what to do if the gateway IP address
: happens to be outside of the netmask IP address range. This can
: happen if the LAN is divided into subnets. All current desktop OS's
: support this, but it seems to be lacking in commodity routers and
: access points. It's not a big problem but should be consdered for
: complex network topologies. (The easy solution is to alias the
: internet gateway router with a LAN gateway IP in each sub-net).

That doesn't happen. The gateway address recognized by the access point
represents only the next level up the subnet tree. So it's always within the
AP's local address space. It's up to the gateway router's WAN side, which the
AP doesn't see, to figure out how to traverse the next step towards the
Internet.

Admittedly I'm ignoring the existence of source-routed packets, but a cheap AP
(which in any case is unlikely to have a choice of gateways) is almost
certainly not going to look at the embedded routing info.
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