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[udlr] Proposal from WIDE Project
This is a simple summary of the WIDE Project's proposal.
Any comments and questions are welcome.
Thank you.
Akihiro Tosaka
Keio University/WIDE Project
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Uni-directional Link Routing with IP tunneling
1. Design
Our policy to resolve UDLR is
to use current routing protocols without any modifications.
The virtual interface scheme is designed as following.
Current routing protocols are designed
on the premise that a station creates a bi-directional link (BDL)
with a neighbor through one interface.
By introducing a virtual interface
that can seperately use uni-directional and bi-directional links,
it is possible to use current routing protocols.
A feed sends packets to the receiver
through uni-directional link (UDL) network.
In the other direction,
a receiver sends packets to the feed
using IP within IP encapsulated through BDL network.
After receiving packets
the receiver decapsulates the IP within IP packets to IP packets.
Using this design,
it is possible for a feed and a receiver to communicate
with each other using UDL.
2. Implementation
The encapsulation of IP within IP
and the implementation of the Virutal Interface [1]
are described in this section.
In order to make the path from the receiver to the feed
look as if they are directly connected by using tunneling,
they both have to know
their own BDL network address and UDL network address,
along with their peer's BDL network address and UDL network address.
A receiver or feed may obtain
its own BDL network address and UDL network address
because the administrater configures them,
but another system is needed to obtain
a peer's BDL network address and UDL network address.
The current implementation employs static configuration,
but dynamic configuration is possible
by using the Dynamic Tunneling Initializing System described later.
When the feed and receiver obtain
the other's BDL network address and UDL network address,
they record the peer's (UDL network address, BDL network address)
in the kernel
and set up the UDL network interface.
The following is an example.
UDL (203.178.140.128/27)
----------------------------------
|(if0: 203.178.140.129) |(if0: 203.178.140.130)
feed receiver
|(if1: 203.178.141.18) |(if1: 203.178.141.196)
| |
| |
-----------(Internet)-------------
At the feed,
the UDL network interface if0 is setup as:
203.178.140.129 netmask 0xffffffe0
the record as:
src bdl address 203.178.141.18,
(dst udl addr 203.178.140.130, dst bdl addr 203.178.141.196)
and the flag indicating the feed is turned on.
The pairs of (dst UDL addr, dst BDL addr) are
provided along the number of receivers.
At the receiver, the UDL network interface if0 is also setup as:
203.178.140.130 netmask 0xffffffe0
the record as:
src bdl address 203.178.141.196,
(dst udl addr 203.178.140.129, dst bdl addr 203.178.141.18)
and the flag indicating the feed is left alone.
3. Routing Protocols
Here, the configuration
when using OSPF as routing protocol and "Gated" as routing program
is described.
Communication from the feed to the receiver is done through UDL.
By setting the interface "if0" in the file "gated.conf" of the feed
to a lower cost than the terrestrial path's one,
the UDL is given priority to a path of the Internet.
On the other hand,
the communication from the receiver to the feed
passes through, in practice, some terrestrial networks.
Because of the overhead of IP within IP tunneling,
this path had better not be used.
Therefore,
by setting interface "if0" in the file "gated.conf" of the receiver
to a higher cost than the terrestiral path's one,
all packets except for those
related to the routing protocols
are denied passage through the tunneling network.
When using RIP as the routing protocol,
it is possible not to be routing information on tunneling path.
The same approach can be used
to other dynamic routing protocols.
4. Summary
(1) Advantages
- It is not necessary to modify other stations because
modifications are needed only at feeds and receivers.
- Current routing protocols may be used without any changes.
(2) Disadvantages
- It is necessary to prepare another system
for a feed and receivers
to obtain the BDL network addresses of each other
to initialize the tunneling path.
To avoid this weeknell,
dynamic tunneling path initilizing is necessary.
This is discussed later.
- The routing information from the receivers to the feed
pass through the tunneling network with an overhead.
But I think it is not so major disadvantage
because the routing traffic is smaller than the data traffic.
5. Dynamic Tunneling Path Initilizing System
(1) A feed sends its own (UDL address, BDL address) to the UDL
at regular intervals.
(2) A new receiver connected to UDL receives the feed's packet,
and then sends its own (UDL address, BDL address) to the feed.
(3) The feed and the receiver know (UDL address, BDL address) each other,
so the tunneling path can be set up.
Details of this system are under consideration.
6. Bibliography
[1] Noritoshi Demizu and Suguru Yamaguchi,
"DDT --- A Versatile Tunneling Technology",
Proceedings of INET'94/JENC5, 1994
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