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OVERVIEW
The checksum used in OSPF (rfc2328) is specified in rc905 annex B. There is an
sample implementation in rfc1008 which forms the basis of the quagga
implementation. This algorithm works perfectly when generating a checksum;
however, validation is a bit problematic.
The following LSA (generated by a non-quagga implementation) is received by
quagga and marked with an invalid checksum; however, it passes both the rfc905
and rfc1008 validation checks.
static uint8_t lsa_10_121_233_29[] = {
0x0e, 0x10, 0x02, 0x03,
0x09, 0x00, 0x35, 0x40,
0x0a, 0x79, 0xe9, 0x1d,
0x80, 0x00, 0x00, 0x03,
0x00, 0x8a, 0x00, 0x1c,
0xff, 0xff, 0xff, 0xe0,
0x00, 0x00, 0x36, 0xb0
};
LS Type: Summary-LSA (IP network)
LS Age: 3600 seconds
Do Not Age: False
Options: 0x02 (E)
Link-State Advertisement Type: Summary-LSA (IP network) (3)
Link State ID: 9.0.53.64
Advertising Router: 10.121.233.29 (10.121.233.29)
LS Sequence Number: 0x80000003
LS Checksum: 0x008a
Length: 28
Netmask: 255.255.255.224
Metric: 14000
You'll note that one byte of the checksum is 0x00; quagga would calculate the
checksum as 0xff8a.
It can be argued that the sourcing implementation generates an incorrect
checksum; however, rfc905 indicates that, for 1's complement arithmetic, the
value 255 shall be regarded as 0, thus either values are valid.
EXPLANATION
The quagga ospfd and ospf6d implementations operate by copying the PDU's
existing checksum in a holding variable, calculating the checksum, and comparing
the resulting checksum to the original. As a note, this implementation has the
side effect of modifying the contents of the PDU.
Evaluation of both rfc905 and rfc1008 shows that checksum validation should
involve calculating the sum over the PDU and checking that both resulting C0 and
C1 values are zero. This behavior is enacted in the rfc1008 implementation by
calling encodecc with k = 0 (checksum offset); however, this functionality had
been omitted from the quagga implementation.
PATCH
This patch adds the ability to call the quagga's fletcher_checksum() with a
checksum offset value of 0xffff (aka FLETCHER_CHECKSUM_VALIDATE) which returns
the sum over the buffer (a value of 0 indicates a valid checksum). This is
similar to the mechanism in rfc1008 when called with k = 0. The patch also
introduces ospf_lsa_checksum_valid().
ospf6d had it's own implementation of the fletcher checksum in
ospf6_lsa_checksum(); it's the same algorithm as in fletcher_checksum(). This
patch removes the local implementation in favor of the library's as well as creates
and uses ospf6_lsa_checksum_valid().
quagga's ISIS implementation suffers from the same problem; however, I do not
have the facilities to validate a fix to ISIS, thus this change has been left to
the ISIS maintainers. The function iso_csum_verify() should be reduced to
running the fletcher checksum over the buffer using an offset of 0.
Signed-off-by: JR Rivers <jrrivers@cumulusnetworks.com>
Reviewed-by: Scott Feldman <sfeldma@cumulusnetworks.com>
Reviewed-by: Nolan Leake <nolan@cumulusnetworks.com>
Reviewed-by: Ayan Banerjee <ayan@cumulusnetworks.com>
Reviewed-by: Shrijeet Mukherjee <shm@cumulusnetworks.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
|
||
|---|---|---|
| .. | ||
| .gitignore | ||
| Makefile.am | ||
| ospf6_abr.c | ||
| ospf6_abr.h | ||
| ospf6_area.c | ||
| ospf6_area.h | ||
| ospf6_asbr.c | ||
| ospf6_asbr.h | ||
| ospf6_flood.c | ||
| ospf6_flood.h | ||
| ospf6_interface.c | ||
| ospf6_interface.h | ||
| ospf6_intra.c | ||
| ospf6_intra.h | ||
| ospf6_lsa.c | ||
| ospf6_lsa.h | ||
| ospf6_lsdb.c | ||
| ospf6_lsdb.h | ||
| ospf6_main.c | ||
| ospf6_message.c | ||
| ospf6_message.h | ||
| ospf6_neighbor.c | ||
| ospf6_neighbor.h | ||
| ospf6_network.c | ||
| ospf6_network.h | ||
| ospf6_proto.c | ||
| ospf6_proto.h | ||
| ospf6_route.c | ||
| ospf6_route.h | ||
| ospf6_snmp.c | ||
| ospf6_snmp.h | ||
| ospf6_spf.c | ||
| ospf6_spf.h | ||
| ospf6_top.c | ||
| ospf6_top.h | ||
| ospf6_zebra.c | ||
| ospf6_zebra.h | ||
| ospf6d.c | ||
| ospf6d.conf.sample | ||
| ospf6d.h | ||
| OSPFv3-MIB.txt | ||
| README | ||
Zebra OSPF daemon for IPv6 network
2003/08/18
README for newer code is not yet. General usage should remain
the same. For further usage, see command helps by typing '?'
in vty, and then imagin ! ;p) Previous README contents follows.
Zebra OSPF daemon for IPv6 network
2001/12/20
Zebra OSPF6d is OSPF version 3 daemon which is specified by
"OSPF for IPv6" (RFC 2740).
*** NOTE ***
Zebra ospf6d is in development yet. It may lack some functionalities,
and may have some bugs. Use the latest version from the anoncvs
repository (http://www.zebra.org/cvs.html) !
This file README is like memo yet, so please feel free to ask
<yasu@sfc.wide.ad.jp> by E-mail. Patches will be appriciated.
ospf6d's vty port was default to 2606/tcp.
Use commands below.
VIEW NODE:
show ipv6 ospf6
To see Router-ID, uptime of ospf6d, some statistics.
show ipv6 ospf6 database ...
This command shows LSA database. You can specify
LS-type/LS-ID/Advertising-Router of LSAs. '*' is recognized.
show ipv6 ospf6 interface ...
To see the status of the OSPF interface, and the configuration
like interface costs.
show ipv6 ospf6 neighbor ...
Shows state of neighbors and choosed (Backup) DR on the I/F.
show ipv6 ospf6 route (X::X)
This command shows internal routing table of the ospf6d.
Routes not calculated by OSPFv3 (like connected routes)
are not shown. If Address is specified (X::X), shows the route
that the address matches.
show ipv6 ospf6 route redistribute (X::X)
Shows the routes advertised as AS-External routes by the router
itself. If Address is specified (X::X), shows the route
that the address matches.
CONFIG NODE:
interface NAME
To enter INTERFACE NODE
router ospf6 ...
To enter OSPF6 NODE
INTERFACE NODE:
ipv6 ospf6 cost COST
Sets the interface's output cost. default 1
ipv6 ospf6 hello-interval HELLOINTERVAL
Sets the interface's Hello Interval. default 10
ipv6 ospf6 dead-interval DEADINTERVAL
Sets the interface's Router Dead Interval. default 40
ipv6 ospf6 retransmit-interval RETRANSMITINTERVAL
Sets the interface's Rxmt Interval. default 5
ipv6 ospf6 priority PRIORITY
Sets the interface's Router Priority. default 1
ipv6 ospf6 transmit-delay TRANSMITDELAY
Sets the interface's Inf-Trans-Delay. default 1
OSPF6 NODE:
router-id A.B.C.D
Sets the router's Router-ID
interface NAME area AREA
Binds interface to specified Area, and start
sending OSPFv3 packets.
Sample configuration is in ospf6d.conf.sample.
--
Yasuhiro Ohara <yasu@sfc.wide.ad.jp>
Kunihiro Ishiguro <kunihiro@zebra.org>