John Scrivner wrote:
Can anyone describe any functional and/or technical differences
between VLANs and say MPLS or Mikrotik's EoIP? It sounds to me like
all three are functional equivalents of each other. Please correct me
if this is an incorrect assumption. I have Googled it so spare me the
obvious. I want to hear your thoughts.
Thanks,
Scriv
VLANs are implemented using (R)STP and they were generally described
earlier. (R)STP is a broadcast protocol that allows multiple layer 2
devices to among other things be connected redundantly without causing
loops. Thus, you can create a rather large and complex network where
individual layer 2 networks share infrastructure, but are separated from
each other. This is used by some carriers to sell layer 2 transport,
which is basically a single VLAN that is trunked across the network.
VLANs are not an ideal way to deal with layer 2 transport for several
reasons. First, STP is very slow to deal with link state changes. Worse,
STP networks get slower the larger they are. RSTP fixes some of these
issues with STP, but convergence time is still too slow for most
applications. Next, VLANs must be properly configured across the all
devices that might be involved in the circuits delivery. Failure to
properly configure the VLANs can result in your entire network failing
as the links are saturated with (R)STP broadcasts. Finally, there is a
finite limit on the number of VLANs you can have on any given Ethernet
network.
MPLS can provide layer 2 transport just like VLANs, but without all the
above problems. However, MPLS is not limited to layer 2 transport. MPLS
allows for transport of many protocols from Ethernet to ATM to IP.
Further, MPLS TE allows for enforcement of SLAs in regards to latency,
jitter, and QoS. Most interestingly though, MPLS rides on top of an IP
network allowing all the benefits of a redundant IP network including
sub-second convergence.
-Matt
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