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The following three rules should be adhered to when configuring EIGRP over an NBMA
cloud such as Frame Relay:
- EIGRP traffic should not exceed the CIR capacity of the virtual
circuit (VC).
- The aggregated traffic EIGRP has 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. In Figure
, the CIR
for each VC is set to 56 Kbps. Since there are four 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. The following are the two main
approaches:
- Take the lowest CIR and multiply this by the number of VCs.
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 reflecting the aggregate CIR of all the circuits.
Three of the VCs have the same CIR, 256 Kbps.
All
three VCs are grouped together as a multipoint subinterface, serial
0/0.1. The single remaining VC, which has a lower CIR, 56 Kbps, can
be assigned a point-to-point subinterface, serial0/0.2.
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