You should follow three
rules when configuring EIGRP over an NBMA cloud such as Frame Relay:
- EIGRP traffic should not exceed
the CIR capacity of the VC (virtual circuit).
- EIGRP's aggregated traffic over
all the VCs should not exceed the access line speed of the
interface.
- The bandwidth allocated to EIGRP
on each VC must be the same in both directions.
If these rules are understood and
followed, EIGRP works well over the WAN. If care is not taken in the
configuration of the WAN, EIGRP can swamp the network.
Configuring Bandwidth over a
Multipoint Network
The configuration of the bandwidth
command in an NBMA cloud depends on the design of the VCs. If the
serial line has many VCs in a multipoint configuration, and all of
the VCs share bandwidth evenly, set the bandwidth to the sum of all
of the CIRs. For example, in Figure ,
each VC's CIR is set to 56 Kbps. Since there are 4 VCs, the
bandwidth is set to 224 (4 x 56).
Configuring Bandwidth over a
Hybrid Multipoint Network
If the multipoint network has differing speeds allocated to the VCs,
a more complex solution is needed. There are two main approaches.
- Take the lowest CIR and multiply
this by the number of VCs. As shown in Figure
,
this is applied to the physical interface. The problem with this
configuration is that the higher-bandwidth links may be
underutilized.
- Use subinterfaces. The bandwidth
command may be configured on each subinterface, which allows
different speeds on each VC. In this case, subinterfaces are
configured for the links with the differing CIRs. The links that
have the same configured CIR are presented as a single
subinterface with a bandwidth, which reflects the aggregate CIR
of all the circuits. In Figure
,
three of the VCs have the same CIR, 256 Kbps. All three VCs are
grouped together as a multipoint subinterface, serial 0.1. The
single remaining VC, which has a lower CIR, 56 Kbps, can be
assigned a point-to-point subinterface, serial 0.2.
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