Maximum count of ms-classless-static-routes

[Glenn Satchell]

This is dhcp's notion of the maximum packet it will send, not the MTU
for the network. According to the source it ranges from a default of
576 up to 1500 bytes. The default size would be close to the size of
your list.

from includes/dhcpd.h

#define DHCP_MTU_MAX            1500
#define DHCP_MTU_MIN            576

There is an option you can set to increase this, but the client has to
be able to accept the larger size, so it may or may not help.

This is from dhcp-options man page:

     option dhcp-max-message-size uint16;

       This option, when sent by the client, specifies  the  max-
       imum  size  of  any  response that the server sends to the
       client.   When specified on the server, if the client  did
       not  send  a dhcp-max-message-size option, the size speci-
       fied on the server is used.   This works for BOOTP as well
       as DHCP responses.

Failing all this, using a packet sniffer will show how the option is
packed in to the packet.

In your list below, you are setting the gateway for all the routes to
be 172,27,19,30. This is the same setting as the 'option routers' for
that subnet, which sets the default gateway. Does your client fail to
set the default gateway? If default gateway setting works then you
shouldn't need all the other static routes as the routing algorithm
will send them to the same gateway.

Can you explain what you are trying to achieve and why you need all the
static routes? There might be a different way to achieve the same
result.

regards,
-glenn

>Subject: Re: Maximum count of ms-classless-static-routes
>From: Yuriy Ohonin <yuriy at krk.ru>
>To: Glenn Satchell <Glenn.Satchell at uniq.com.au>, Users of ISC DHCP 
<dhcp-users at lists.isc.org>
>Date: Thu, 09 Jul 2009 11:49:17 +0800
>
>On Thu, 2009-07-09 at 13:29 +1000, Glenn Satchell wrote:
>> There is a limit to how big a DHCP packet can be, and this can limit
>> the total size of all the options. 
>As for as i know, maximum packet size is 4KB. This is much more than 31
>routes even in big unoptimazed string format. Maybe, i'm wrong, what is
>the maximum packet size in this case?
>
>> Suggest you set up the router to
>> know all the routes if possible, and only give the client pc a default
>> route to that router.
>Thanks, but this is not possible :(
>> 
>> regards,
>> -glenn
>> 
>> >Subject: Maximum count of ms-classless-static-routes
>> >From: Yuriy Ohonin <yuriy at krk.ru>
>> >To: dhcp-users at lists.isc.org
>> >Date: Thu, 09 Jul 2009 11:16:41 +0800
>> >
>> >Hello,
>> >
>> >I'm not able to set more than 31 static routes via dhcpd.
>> >(using "option ms-classless-static-routes")
>> >Well, i can write config file, but client pc (os windows xp home) does
>> >not accept them.
>> >
>> >Here is the config:
>> >
>> ># New_Subnet_3824
>> > subnet 172.27.19.0 netmask 255.255.255.224 {
>> >        authoritative;
>> >        option domain-name "orionnet.ru";
>> >        option domain-name-servers 80.65.20.1,80.65.16.1;
>> >        option routers 172.27.19.30;
>> >        deny unknown-clients;
>> >
>> >option ms-classless-static-routes 23, 62,33,58, 172,27,19,30, 23,
>> >62,33,66, 172,27,19,30, 24, 62,213,55, 172,27,19,30, 24, 62,213,56,
>> >172,27,19,30, 21, 79,99,216, 172,27,19,30, 27, 80,82,189,32,
>> >172,27,19,30, 21, 80,91,192, 172,27,19,30, 24, 80,91,207, 172,27,19,30,
>> >24, 80,237,84, 172,27,19,30, 24, 80,237,107, 172,27,19,30, 23,
>> >80,240,34, 172,27,19,30, 24, 83,234,36, 172,27,19,30, 24, 83,234,173,
>> >172,27,19,30, 28, 83,234,173,128, 172,27,19,30, 21, 84,22,128,
>> >172,27,19,30, 21, 84,22,136, 172,27,19,30, 24, 84,22,136, 172,27,19,30,
>> >24, 84,22,137, 172,27,19,30, 24, 84,22,138, 172,27,19,30, 24, 84,22,139,
>> >172,27,19,30, 28, 84,22,139,224, 172,27,19,30, 24, 84,22,140,
>> >172,27,19,30, 24, 84,22,141, 172,27,19,30, 24, 84,22,142, 172,27,19,30,
>> >24, 84,22,143, 172,27,19,30, 21, 84,22,144, 172,27,19,30, 24, 84,22,152,
>> >172,27,19,30, 24, 84,22,154, 172,27,19,30, 24, 84,22,155, 172,27,19,30,
>> >24, 84,22,156, 172,27,19,30, 24, 84,22,157, 172,27,19,30, 24, 84,22,158,
>> >172,27,19,30, 24, 84,22,159, 172,27,19,30, 29, 87,103,152,96,
>> >172,27,19,30, 22, 87,236,40, 172,27,19,30;
>> >option rfc3442-classless-static-routes 23, 62,33,58, 172,27,19,30, 23,
>> >62,33,66, 172,27,19,30, 24, 62,213,55, 172,27,19,30, 24, 62,213,56,
>> >172,27,19,30, 21, 79,99,216, 172,27,19,30, 27, 80,82,189,32,
>> >172,27,19,30, 21, 80,91,192, 172,27,19,30, 24, 80,91,207, 172,27,19,30,
>> >24, 80,237,84, 172,27,19,30, 24, 80,237,107, 172,27,19,30, 23,
>> >80,240,34, 172,27,19,30, 24, 83,234,36, 172,27,19,30, 24, 83,234,173,
>> >172,27,19,30, 28, 83,234,173,128, 172,27,19,30, 21, 84,22,128,
>> >172,27,19,30, 21, 84,22,136, 172,27,19,30, 24, 84,22,136, 172,27,19,30,
>> >24, 84,22,137, 172,27,19,30, 24, 84,22,138, 172,27,19,30, 24, 84,22,139,
>> >172,27,19,30, 28, 84,22,139,224, 172,27,19,30, 24, 84,22,140,
>> >172,27,19,30, 24, 84,22,141, 172,27,19,30, 24, 84,22,142, 172,27,19,30,
>> >24, 84,22,143, 172,27,19,30, 21, 84,22,144, 172,27,19,30, 24, 84,22,152,
>> >172,27,19,30, 24, 84,22,154, 172,27,19,30, 24, 84,22,155, 172,27,19,30,
>> >24, 84,22,156, 172,27,19,30, 24, 84,22,157, 172,27,19,30, 24, 84,22,158,
>> >172,27,19,30, 24, 84,22,159, 172,27,19,30, 29, 87,103,152,96,
>> >172,27,19,30, 22, 87,236,40, 172,27,19,30;
>> >
>> >
>> ># ussa60 1-2
>> >        host orion_14 {
>> >                hardware ethernet 00:22:15:15:ae:5a ;
>> >                fixed-address 172.27.19.2 ; }
>> >}
>> >