CISCO-CEF-MIB

Cisco Express Forwarding (CEF) describes a high speed switching mechanism that a router uses to forward packets from the inbound...

  • Organization:

    Cisco System, Inc.

  • Module:

    CISCO-CEF-MIB

  • Version:

    2006-01-30

  • File:

    CISCO-CEF-MIB.yang

  • Abstract:

    Cisco Express Forwarding (CEF) describes a high speed switching mechanism that a router uses to forward packets from the inbound...

  • Contact:

    Postal: Cisco Systems, Inc.
    170 West Tasman Drive
    San Jose, CA 95134-1706
    USA

    Tel: +1 800 553-NETS

    E-mail: cs-cef@cisco.com

  • Check for an additional details:

    YANG Catalog

  • Description:

    Cisco Express Forwarding (CEF) describes a high speed
    switching mechanism that a router uses to forward packets
    from the inbound to the outbound interface.

    CEF uses two sets of data structures
    or tables, which it stores in router memory:

    Forwarding information base (FIB) - Describes a database
    of information used to make forwarding decisions. It is
    conceptually similar to a routing table or route-cache,
    although its implementation is different.

    Adjacency - Two nodes in the network are said to be
    adjacent if they can reach each other via a single hop
    across a link layer.

    CEF path is a valid route to reach to a destination
    IP prefix. Multiple paths may exist out of a router to the
    same destination prefix. CEF Load balancing capability
    share the traffic to the destination IP prefix over all
    the active paths.

    After obtaining the prefix in the CEF table with the
    longest match, output forwarding follows the chain of
    forwarding elements.

    Forwarding element (FE) may process the packet, forward
    the packet, drop or punt the packet or it may also
    pass the packet to the next forwarding element in the
    chain for further processing.

    Forwarding Elements are of various types
    but this MIB only represents the forwarding elements of
    adjacency and label types. Hence a forwarding element
    chain will be represented as a list of labels and
    adjacency. The adjacency may point to a forwarding element
    list again, if it is not the last forwarding element in this
    chain.

    For the simplest IP forwarding case, the prefix entry will
    point at an adjacency forwarding element.
    The IP adjacency processing function will apply the output
    features, add the encapsulation (performing any required
    fixups), and may send the packet out.

    If loadbalancing is configured, the prefix entry will point
    to lists of forwarding elements. One of these lists will be
    selected to forward the packet.

    Each forwarding element list dictates which of a set of
    possible packet transformations to apply on the way to
    the same neighbour.

    The following diagram represents relationship
    between three of the core tables in this MIB module.

    cefPrefixTable cefFESelectionTable

    +---------------+ points +--------------+
    | | | | a set +----> | | | | |
    |---------------| of FE | |--------------|
    | | | | Selection | | | | | |
    |---------------| Entries | |--------------|
    | | | |------------+ | |<----+
    |---------------| |--------------| |
    | | +--------------| | | | | |
    +---------------+ | +--------------+ |
    | |
    points to an |
    adjacency entry |
    | |
    | cefAdjTable |
    | +---------------+ may point |
    +->| | | | to a set |
    |---------------| of FE |
    | | | | Selection |
    |---------------| Entries |
    | | | |----------------+
    |---------------|
    | |
    +---------------+

    Some of the Cisco series routers (e.g. 7500 & 12000)
    support distributed CEF (dCEF), in which the line cards
    (LCs) make the packet forwarding decisions using locally
    stored copies of the same Forwarding information base (FIB)
    and adjacency tables as the Routing Processor (RP).

    Inter-Process Communication (IPC) is the protocol used
    by routers that support distributed packet forwarding.
    CEF updates are encoded as external Data Representation
    (XDR) information elements inside IPC messages.

    This MIB reflects the distributed nature of CEF, e.g. CEF
    has different instances running on the RP and the line cards.

    There may be instances of inconsistency between the
    CEF forwarding databases(i.e between CEF forwarding
    database on line cards and the CEF forwarding database
    on the RP). CEF consistency checkers (CC) detects
    this inconsistency.

    When two databases are compared by a consistency checker,
    a set of records from the first (master) database is
    looked up in the second (slave).

    There are two types of consistency checkers,
    active and passive. Active consistency checkers
    are invoked in response to some stimulus, i.e.
    when a packet cannot be forwarded because the
    prefix is not in the forwarding table or
    in response to a Management Station request.

    Passive consistency checkers operate in the background,
    scanning portions of the databases on a periodic basis.

    The full-scan checkers are active consistency checkers
    which are invoked in response to a Management Station
    Request.

    If 64-bit counter objects in this MIB are supported,
    then their associated 32-bit counter objects
    must also be supported. The 32-bit counters will
    report the low 32-bits of the associated 64-bit
    counter count (e.g., cefPrefixPkts will report the
    least significant 32 bits of cefPrefixHCPkts).
    The same rule should be applied for the 64-bit gauge
    objects and their assocaited 32-bit gauge objects.

    If 64-bit counters in this MIB are not supported,
    then an agent MUST NOT instantiate the corresponding
    objects with an incorrect value; rather, it MUST
    respond with the appropriate error/exception
    condition (e.g., noSuchInstance or noSuchName).

    Counters related to CEF accounting (e.g.,
    cefPrefixPkts) MUST NOT be instantiated if the
    corresponding accounting method has been disabled.

    This MIB allows configuration and monitoring of CEF
    related objects.

© 2023 YumaWorks, Inc. All rights reserved.