38th IETF - Memphis, TN, USA
Reported by: Walid Dabbous - Thanks to Scott Michel and Jean Bolot for taking
notes.
No special comment
Walid presented the general problem and the two solutions for routing with udl, namely: modify routing protocols (referred to later as RPM, or Routing Protocol Modification) or tunneling.
Major udlr problems: dynamic discovery of feeds and receivers, exchange of information between feeds and recveivers (how, what to exchange?)
Receivers are supposed to detect the feeds directly, and senders generate "appropriate" routing information so that receivers send along the backchannel and receive along the feed.
Two approaches: routing protocol modifications or tunneling.
Presents VIPRe (proposed I-D describing it available).
Dynamic discovery of a feed via a new ICMP message.
Routing information from feeds is processed by receivers.
Metric of the backchannel is set dynamically as required.
Implementation available (at the UCLA mirror site)
Proposed I-D on "Unidirectional Link routing with IP tunneling"
Another proposed I-D on dynamic tunneling soon to come
Implementation: RIP2, OSPF, DVMRP done in domestic testbed
BPG-4 will be tested in international testbed
In testbed, set metrics so that shortest path is as desired
Shows setups for DVMRP, seems to work fine (static metric setup though)
Then shows geographical status
Multicast over NASA ACTS satellites; trying out ULDR multicast
UDLR testbed in Hughes Research Labs using 11 PCs (FreeBSD) to create complex
satellite network environments.
Transmission of IP packets over DVP-MPEG
One feed and one receiver with Ethernet bidirectional link, currently static
configuration
IP address used to filter packets
Second receiver in Paris, eventually to include the MERCI project.
If focus on tunneling for short term, then need to address the question: Is tunnelling sufficient to solve udlr?
Several issues to discriminate between the two approaches:
1. Dynamic Routing
(already discussed: which metric to use?)
2. Automatic Configuration, i.e. possibility for feeds and receivers to detect each other: trivial with RPM and ICMP Relay Discovery with tunnelling.
Question: Why do we need another ICMP message? Walid points out that VIPRe uses a mechanism inspired from router discovery as documented by Deering - interrogator wants WG to use accepted methods and mechanisms instead of inventing yet another.
During the discussion of the second issue (automatic configuration), WIDE presented their Dynamic Tunneling Path Configuration approach:
Automatic initiation of tunneling path: When a feed is up or a new receiver joins, a tunneling path is automatically established. Periodically detects the UDL for an unexpected death of feed or receiver: When the feed (receiver) goes down unexpectedly, the receiver (feed) detects it and the tunneling path is canceled by using the Life Time of Tunneling Path (LTTP). When the feed or the receiver goes away, the UDL is downed automatically: Before the feed (receiver) leaves the UDL, the feed (receiver) sends the "close message" to terminate the tunneling path.
This triggers discussion on amount of state per receiver. If the the feed (receiver) sends "close" message to terminate the tunnel -> should have per receiver state/traffic at feeds.
Christian Huitema points out that there is no need for per receiver state at the feed, but only something that allows demuxing (to make feed believe that info came back over the satellite link). Confirmation from Aerospace.
It was pointed out that you might need state anyway for tunnel security; however, you can design for authentication.
Also question about relevance of explicit msgs to detect unexpected death of link (Aerospace says implicit discovery should be enough e.g. by soft state update).
Bob Lindell pointed out that dynamic discovery is important in the multiple feed case. This isn't necessarily true in the single feed case. Walid points out that the support of multiple feeds should be an important feature of whatever drafts come out of the WG.
3. Routing Efficiency
There should be no "imposed" encapsulation for traffic sent by receivers to hosts on the Internet (contrary to what's done by DirecPC and Berkeley). No pb for the RPM and tunnelling (use bidir interface to route traffic).
Discussion on sending things encapsulated or not encapsulated. It was pointed that encapsulation has no major performance problem, and encapsulating everything makes things consistent.
In VIPRe, the issue of whether or not to route via the feeds is left as a local decision.
Tunnels are set up to hide the topology; this affects the original IP header (such as TTL). Impact analysis should take into account the transport and application layers, i.e. traffic which is tunneled through non-RSVP aware routers for RSVP traffic.
C. Huitema brought up the problem of layering. Also proposed that feeds have several IP addresses so that the receivers choose whether or not to encapsulate.
4. Support IP mcast forwarding:
RPF ensures that shortest path routing happens if the reverse metric is used. But with "classical" tunneling we have asymmetric metrics. This should not be the case for DVMRP. Back channel metric should be chosen equal to the
"forward" satellite link metric for DVMRP. On the other hand, no multicast traffic is forwarded on the virtual back channel to avoid duplication.
Hidetaka Izu said that it is not necessary to have this equality by showing the example in the WIDE slides.
However, metric setting could be a problem. C. Huitema says DVMRP looks OK for now (still some work for setting metrics, but you could have something semi-automatic like feed = 32, router = 1).
C. Huitema pointed out another open point, when the receiver is a host, not a router. You need to support IGMP-like functionality between hosts and feeds.
C. Huitema pointed out that CBT might be a better solution for multicast, where the root of the CBT is the satellite feed.
5. scalability
6. interdomain routing:
receivers likely in different AS; what nets should they announce? That's dealt with by BGP.
7. applicability to other udl areas:
maybe IP over cable.
8. Other issues:
ARP: did not condider yet because IP over DVB standard not supported. (currently IP address used for both media and IP address in the INRIA implementation). The IP over DVB standard will be implemented.
Huitema pointed out that ARP does not run over IP whereas tunnel provides IP level. Might have to resort to an IP v6 mechanism.
GRE may be used as a solution. This brought the question of which tunneling protocol to use: currently IP-in-IP is widely used, but someone proposed using GRE which handles the ARP case. IP-in-IP could also be extended to handle the ARP case.
Also what about IPv6? Agreed solution?
Consensus appears to be on tunneling, and it must handle the multicast routing case (IGMP), and ARP.
To extend the WG for a mesh of udl links then possibly start a new WG for addressing the general udl routing problem after udlr ends. To be discussed later.
Existing: VIPRE, WIDE, INRIA
Should they be adopted individually and label them as UDLR I-D's? (YES)
Should make sure that they don't look like results; they should look like proposals. suggest 1pp boilerplate that indicates proposalness.
Edit a common ID on a single agreed tunnelling solution:
Edit "issues" ID, post all IDs before end of May
Cross-post "issues" ID to other lists
INRIA may be able to demonstrate UDLR multicast over the Eutelsat satellite to show either the UDLR IETF session or the SIGCOMM '97 keynote or both.
W. Dabbous slides are available at ftp://ftp-sop.inria.fr/rodeo/udlr/slides/general38.ps.gz
Izumiyama Hidetaka slides are available at ftp://ftp-sop.inria.fr/rodeo/udlr/slides/wide38.ps.gz
Walid Dabbous