OSPF Abnormal State Information
FutureweiBoston, MAUSAHuaimo.chen@futurewei.comFutureweiBoston, MAUSAHuaimo.chen@huawei.com
General
Internet Engineering Task Forcetemplate
This document describes a couple of options for an OSPF router
to advertise its abnormal state information in a routing domain.
There may be some states that are not normal in an OSPF router,
which include the state that a link state advertisement (LSA) stays
in a retransmission list on the router for more than a given time period
such as more than hello dead interval, and may include
the state that a database description (DD) packet does not
get acknowledged for a given period of time.
If a link state advertisement (LSA) with a topology change in a router
can not get through over an OSPF interface for a given time period,
some of the routers in the routing domain may have different view
of the real network topology, thus routing loops may occur and some
traffic may get dropped.
It is useful for an OSPF router in a routing domain to
advertise its abnormal state information to other routers,
or notify some systems such as an event management or
monitoring system for its abnormal state.
This document describes a couple of options for an OSPF router
to advertise its abnormal state information in a routing domain.
This document uses terminologies defined in RFC 4970, RFC 2328,
and RFC 2740.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
OSPF routers MAY advertise their state information in
a area-scoped or AS-scoped router state information LSA
with a router state informatioin TLV.
OSPFv2 routers will advertise an area-scoped or AS-scoped
Router State Information Opaque-LSA [RFC 2370], which
has an Opaque type of 5 and Opaque ID of 0.
The RSI LSA will be originated initially by an OSPF router
when an OSPF instance is created and re-originated
in every refresh interval (LSRefreshTime) with the current
state information of the router.
When the current state information changes, the RSI LSA will also
be originated.
The format of the TLVs within the body of a RSI LSA is the same as
the format used by the Traffic Engineering Extensions to OSPF [RFC 3630].
The LSA payload consists of one or more nested Type/Length/Value
(TLV) triplets. The format of each TLV is:
The Length field defines the length of the value portion in octets
(thus a TLV with no value portion would have a length of 0). The TLV
is padded to 4-octet alignment; padding is not included in the length
field (so a 3-octet value would have a length of 3, but the total
size of the TLV would be 8 octets). Nested TLVs are also 32-bit
aligned. For example, a 1-byte value would have the length field set
to 1, and 3 octets of padding would be added to the end of the value
portion of the TLV. Unrecognized types are ignored.
TBD.
A router advertising a RSI LSA MAY
include the Router State Information TLV. If included, it
MUST be the first TLV in the LSA. Additionally, the TLV MUST
accurately reflect the OSPF router's state information in the scope
advertised.
The format of the Router State Information TLV is as follows:
The format of the Router State Information LSA retranmission time
sub-TLV is as follows:
Type A 16-bit field set to 1.
Length A 16-bit field that indicates the length of the value
portion in octets and will be 2.
Value A 16-bit field set to the current maximum time
(in seconds) that an LSA stays in a retransmission
list in a router.
The format of the sub-TLV for the maximum time that a Database
Description packet is not acknowledged is illustrated below.
Type A 16-bit field set to 2.
Length A 16-bit field that indicates the length of the value
portion in octets and will be 2.
Value A 16-bit field set to the current maximum time
(in seconds) for which a DD packet is not acknowledged
in a router.
Instead of using a Router State Information LSA to advertise the
abnormal state information for a router,
we may use the existing Router Information
LSA defined in RFC 4970 to advertise the state information
through adding the Router State Information (RSI) TLV into
the Router Inforamtion LSA.
When a Router State Information (RSI) TLV is put into a Router
Information LSA, the type of the TLV may be different from the one
mentioned in the section above.
An OSPF router may also notify other systems such as
an event management system about its abnormal state
when the abnormal state occurs in the router.
The mechanism described in this document does not raise any new
security issues for the OSPF protocols.
tb
The author would like to thank people
for their valuable comments on this draft.