Dynamic Routing Guide
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The UM Router uses interfaces, called portals, through which to pass data. A UM Router consists of two or more bidirectional portals that may be one of two types:
The figure below shows a simple UM Router use case, where two UM Routers bridge an ISP to connect two TRDs.
You configure portals in the UM Router's XML configuration file, specifying the portal's name, cost, UM Configuration, Access Control Lists and other attributes. See XML Configuration Reference.
Since topic resolution uses UDP, sources and receivers must have UDP connectivity to each other. When they do, we consider them to be in the same topic resolution domain (TRD). More specifically, UM contexts must satisfy the following two requirements to belong to the same topic resolution domain.
For example, two contexts on separate machines in the same LAN are not in the same topic resolution domain if they use different resolver addresses. See Multicast Resolver Network Options. A topic resolution domain can span a WAN if the UM contexts on each side of a firewall use the same UM configuration and the firewall allows UDP traffic (multicast or unicast) to pass.
Each endpoint portal must identify its associated topic resolution domain with a domain-id the UM Router's XML configuration file, as in the example below. All portals in the same TRD must have the same domain-id, and different TRDs networked together via UM Routers must have domain-ids unique to each other.
To resolve a topic across a UM Router (described in Basic UM Router Operation), the UM Router creates, within portals, proxy sources and proxy receivers (shown in the figure below by their dashed lines). These proxies behave like their UM counterparts; they resolve topics on the TRDs like normal sources and receivers, and the UM Router internally passes data from one portal to the other. However unlike regular sources, proxy sources do not have retransmission retention buffers normally used for Late Join or OTR.
Portals exist while the UM Router is running, however, the UM Router creates proxy sources and receivers during topic resolution and deletes them when the topic is retired.
In multiple-UM Router environments where more than one UM Router can provide possible messaging pathways, the UM Routers are able to cooperatively determine and establish optimal routes. Also, the UM Router network is able to detect link or other UM Router outages and automatically reroute traffic as needed. See Routing Topologies for more information.