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Unlike RIP route advertisements, DVMRP routes are sent in an
abbreviated format, as shown in Figure 5-18. Route advertisements
consist of three components: the netmask, the network, and the
metric. The netmask is assumed to be of the form 255.x.x.x because
the standard subnet masks for class A, B, and C addresses begins
with 255. Because the first octet of every subnet mask is assumed to
be 255, then the first octet does not need to be included in the
route report. This is why the length of the netmask fields in Figure
5-18 is shown as only three bytes. For example, if the netmask in
the route report has a value of 255.255.128, then the full netmask
has the value 255.255.255.128. |
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