Multiple subnets with classes - 'option routers' issue
Gundares
vanchik at yandex.ru
Sat Jun 7 16:15:48 UTC 2008
Dear dhcp-users,
first, the essence - the isc-dhcpd provides the default router
configured in the first subnet declaration for clients from other
subnets.
Here are the details.
I'm using isc-dhcpd 3.0.5 under FreeBSD-6.3.
There are two CMTSes at the customer site with three (total) cable
interfaces, two IP-subnets on each interface (one for modems, another
for PCs). So, CMTSes are acting as dhcp-relays (they are routers).
Cable modems are getting IP and its config-files depending on classes
Classes are declared like this:
subnet 172.16.0.0 netmask 255.255.248.0 {
.. <some 'global' options common for all types of cable modems>
.. <i.e. time server, time offset, log server, etc>
option routers 172.16.0.1;
..
..
class "SB5100" {
match if (MOTO.modnum = "SB5100"); # this is suboption 9 of option 43
filename "sb5100.bin"
}
class "EPX2203"
match if (MOTO.modnum = "EPX2203";
filename "epx2203.bin";
}
pool {
allow members of "SB5100";
allow members of "EPX2203";
deny members of "SB5100-UPG";
range 172.16.0.50 172.16.7.254;
}
pool {
deny members of "SB5100";
deny members of "EPX2203";
allow members of "SB5100-UPG";
range 172.16.0.10 172.16.0.49;
}
}
This dhcpd-config was working fine for many years (for only one CMTS),
but two days ago client bought the second one. So, I've added new
subnets with the same class-definitions (now dhcpd logs error: 'too many
classes match MODEM_MAC_ADDR'). After that, the cable modem connected
with the second CMTS (subnet 172.17.0.0/18), gets all the options
properly, except the default router option - 172.16.0.1 (this is the
first CMTS' cable interface primary IP-address).
tcpdump`ed OFFER packet looks like this:
2008-06-07 18:23:09.001689
IP (tos 0x0, ttl 64, id 53242, offset 0, flags [none],
proto: UDP (17), length: 336, bad cksum 0 (->fb94)!)
<MY_SERVER'S_IP>.67 > 172.17.0.1.67:
[bad udp cksum 648!] BOOTP/DHCP, Reply,
length: 308, hops:1, xid:0x167cd60d, flags: [Broadcast] (0x8000)
Your IP: 172.17.31.254
Server IP: <MY_SERVER'S_IP>
>>>>>> Gateway IP: 172.17.0.1
Client Ethernet Address: 00:1a:ad:71:1a:b4
file "sb5100.bin"
Vendor-rfc1048:
DHCP:OFFER
SID:<MY_SERVER'S_IP>
LT:86400
SM:255.255.192.0
TZ:14400
>>>>>> DG:172.16.0.1
TS:<MY_SERVER'S_IP>
LOG:<MY_SERVER'S_IP>
NS:<MY_SERVER'S_IP>
ACKT:1.4.128.1.0.3.2.6.0.26.173.113.26.180
So, how can I set the _proper_ default gateway address for clients?
--
Regards,
Ivan V. Borodin <ivan at vimcom.ru>
Computer Systems Engineer
JSC "Vimcom Optic TS"
p. +7(495)-737-37-57
f. +7(495)-737-37-55
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