duncan@comp.vuw.ac.nz (Duncan McEwan) (05/26/88)
I need to find out what products are available for linking two geographically remote LAN's via a public x.25 network. I have advertising glossies for Sun's SunLink X.25 product which seems to provide the desired facilities, but which leaves some questions unanswered. From what I can tell SunLink X.25 does allow carrying IP packets from one lan to another via an x.25 virtual circuit. What I would like to know is how transparent this is. Does one host on the local ip lan (not necessarily the Sun running SunLink x.25) just ask to send an ip packet to a node on the remote lan, causing SunLink X.25 to open a VC to transmit the packet? Assuming this is the way it works, does SunLink multiplex datagrams from several tcp or udp sources over the one VC, and if so, at what point does it close the VC? Are the local and remote lans on different class C ip networks (I guess they must be to allow packets to be routed to the host with the x.25)? How are the ip addresses mapped into x.121 addresses? Finally from an economic point of view how reasonable is it to send ip over x.25 bearing in mind the relatively large tcp + ip headers, particularly when you are paying for both connect time and number of segments sent (a segment is 64 octets, and NZ telcoms charge for unfilled segments as one full one). Enough about SunLink x.25 specifically! Are there any other products (bridges, routers, other computer vendors x.25 packages) that offer this type of functionality. In particular, do HP offer anything similar? Can one companies product interoperate with anothers (for example, I believe that the Multinet IP/TCP package for VMS does/will offer some facility for tcp/ip over x.25 - is it reasonable to expect a Sun running SunLink x.25 to be able to talk IP with it). I think that is enough questions for one article! Any answers to some or all of the above will be appreciated. Answer by email and if there is any demand I will summarise. --- Duncan Domain: duncan@comp.vuw.ac.nz Path: ...!uunet!vuwcomp!duncan
melohn%sluggo@Sun.COM (Bill Melohn) (05/29/88)
In article <13652@comp.vuw.ac.nz> duncan@comp.vuw.ac.nz (Duncan McEwan) writes: >From what I can tell SunLink X.25 does allow carrying IP packets from one lan >to another via an x.25 virtual circuit. What I would like to know is how >transparent this is. Does one host on the local ip lan (not necessarily the >Sun running SunLink x.25) just ask to send an ip packet to a node on the >remote lan, causing SunLink X.25 to open a VC to transmit the packet? The X.25 virtual circuit is treated exactly the same as a dedicated serial line connecting two IP hosts together. Routing information about networks on either side of the link is passed across the link via the standard Unix RIP. In the resulting internet, any host can access any other host using whatever IP based services are desired (note, protocols like NFS require some mount parameter tweaking in order to not timeout over slower, long haul links). >Assuming this is the way it works, does SunLink multiplex datagrams from >several tcp or udp sources over the one VC, and if so, at what point does it >close the VC? Are the local and remote lans on different class C ip networks >(I guess they must be to allow packets to be routed to the host with >the x.25)? How are the ip addresses mapped into x.121 addresses? >Finally from an economic point of view how reasonable is it to send ip >over x.25 bearing in mind the relatively large tcp + ip headers, >particularly when you are paying for both connect time and number of >segments sent (a segment is 64 octets, and NZ telcoms charge for >unfilled segments as one full one). As explained above, each VC is treated like a virtual point to point wire connecting each pair of hosts via the public data network. Each VC used for IP has a network interface associated with it, with an IP address of its own. An X.25 circuit manager user process is provided, which establishes the X.25 virtual circuits to each of the remote hosts based on a config file, and binds the VCs to the IP network interfaces used by the kernel routing code. The manager attempts to keep the VCs connected all the time. This can be expensive if you are paying for connect time, but since processes like the routing daemon tend to wake up and send information on a regular basis, the IP circuits tend to stay active even when they aren't actively being used for user data transfer. We are investigating ways to make it practical to create X.25 virtual circuits only when needed for end-user data transfer, while still maintaining full routing capabilities and connectivity information. Our implementation of X.25 Standard services does this on the DDN, where the X.121 to IP address mapping is fixed, and where routing can be done by use of a default route to, and redirects from, a core gateway.
jh@tut.fi (Juha Hein{nen) (06/01/88)
SunLink X.25 indeed allows connecting two IP networks over X.25 but it requires a PVC and cannot dynamically open and close the connection. You may want to check the Cisco router product that also has the later capability. -- Juha Heinanen, Tampere Univ. of Technology, Finland jh@tut.fi (Internet), tut!jh (UUCP), jh@tut (Bitnet)