class-B netmask on BEFSR41

Discussion in 'Cisco/Linksys Wireless Routers' started by sj__1, Apr 25, 2006.

  1. sj__1

    sj__1 LI Guru Member

    I can assign a class-B LAN address (say to my
    ("v1") BEFSR41 but the LAN netmask pull-down menu only
    offers me class-C choices (,, ...).

    Does anybody know how to get a BEFSR41 to have a LAN-side
    netmask which is class-B, say

    I am interested in hearing any solution, whether supported by
    Linksys or not.

    Thanks in advance.
  2. Mikedd

    Mikedd LI Guru Member

    Class B subnet mask

    I asked Linksys tech support about that issue. They just don't support anything but class C subnet masks. I believe the theory is that these are consumer oriented, access routers supporting a few ports, so that Class C is what you get.

    I don't believe that you are going to be able to configure the router to support a class B subnet unless you hack the firmware, and then you will not get any support from Linksys (small loss).
  3. Toxic

    Toxic Administrator Staff Member

    afaik linksys only use Class C due to their products are for home users.

    If you want Class B or A you got to pay for it.
  4. fjb

    fjb Networkin' Nut Member

    These are all krud answers.

    RFC1918 specifies the address space and associated network masks. The choice of address space is not directly indicative of the number of hosts actually being used. The network mask affects only the number of *available* host addresses, there is absolutely no implication that all of these host addresses are *stored* within the router's RAM; the (mask&hostaddr) operation is an on-the-fly calculation used to determine if the packet requires routing (e.g. should be sent to the WAN interface) or can be delivered locally without consulting the routing table.

    The network configuration implementation in the BEFSR41 is flawed, and Cisco well knows this (look at the author list on RFC1918 ..., and contact Yakov if you doubt that). Best practices under RFC1918 include the following statements:
    If a suitable subnetting scheme can be designed and is supported by
    the equipment concerned, it is advisable to use the 24-bit block
    (class A network) of private address space and make an addressing
    plan with a good growth path. If subnetting is a problem, the 16-bit
    block (class C networks), or the 20-bit block (class B networks) of
    private address space can be used.
    Note that even the private 192.168 space is a /16 (not a /24). The point of using private address space is to allow for flexibility. Sure, the statement includes the condition "is supported by the equipment concerned", but sites don't keep the same equipment installed permanently -- so it is important that the router supports the *standard* so that customers aren't required to renumber their entire network after changing to a new router! C'mon!

    I didn't come to this site to flame anyone, I came here looking for a way to hack the stupid Linksys BEFSR41 firmware to allow the correct netmask. Seems that there might be a way to binary patch the firmware with the correct netmasks (i.e. overwrite the "standard" netmask table in the GUI with more useful values, e.g.

    That's the question that needs to be answered: Can the 2.00.2 Firmware for BEFSR Ver. 4.3 be binary patched to allow configuration of different netmasks, thereby supporting networks of /8, /9, /10, ..., allowing more generally useful values? IF NOT, then is it possible to define static routing table entries in this router to have it FORWARD to another machine that will support this configuration?

    E.g., Is the following configuration in the BEFSR41/v4.3/fw2.00.2 supported, and if so will it have the desired effect of allowing routing to the entire /8 network via the attached gateway host?
    LAN / (/30 net, smallest allowed by config)
    Static routes:
    Entry: (1)
    Name: ClassA_Slash8
    Gateway: (a local host with "IP Forwarding" enabled)
    Hopcount: 0
    Interface: LAN

    Alternatively, do the RIP1 and/or RIP2 configurations within the BEFSR41/v4.3/fw2.00.2 work correctly to support the above configuration (using a unix/linux box to handle the internal gateway/rip under quagga)?

    I do not have a BEFSR41 available to test these, but I would appreciate a response from someone who *does* have this router available. I am asking this prior to using this particular router as a replacement for a larger (and more power-intensive) router that is already in use. The issue is not having more than 255 hosts (and even if it were, the arp table size will never approach 255 simultaneous hosts within the requisite timeouts), the issue is avoiding the need to renumber the entire network!

    Thanks in advance,
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