In the previous couple of videos, we walked through configuring EAGRP with
traditional mode and name
mode. And in this video, I'd like to walk you through using the option of
variance for unequal cost
load balancing inside EAGRP. I'm going to show you how to do it on either
flavor of implementation
named or traditional. Now, by default, a router like R4 or any other router
running EAGRP,
if it has two or three routes that have the same exact metric and it's the best
for the lowest
metric for a specific destination, it will automatically install and start
using those equal cost WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
using those equal cost
paths. But in the event, R4 has a successor route that goes this way and then
feasible successor
routes to go this way and that way, we could tell R4 that we want to go ahead
and start using
additional potential paths and start doing load balancing across all of them.
Now, here's how it
works. Let's imagine that the successor route has a metric of 10. So I know
that's a small number in EAGRP,
but it's easier to look at and talk about. So if that's the successor metric,
let's imagine we have
feasible successor one that has a metric of 11 and we have feasible successor WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
feasible successor one that has a metric of 11 and we have feasible successor
two that has a metric
of, let's say, 19 and let's say feasible successor three has a metric of, let's
say, 21. Now, if this
is our successor metric of 10, we're going to use a command called variance.
Variant simply says
to the router that you configured on how bad can a route be. So if we said the
variance is two,
that means that if we take the successor route and it's metric of 10 and we
multiply that by two,
which would be 20, it says basically any feasible successor that met that feas WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
which would be 20, it says basically any feasible successor that met that feas
ibility condition,
any feasible successor that have a metric of 20 or less. So that would work and
that would work
can also be used and they can start load balancing across all three of those
paths for the destination
8888, for example. However, the feasible successor three because it's more than
two times higher
is 21 and so it's just above that threshold because it's higher than that
threshold, it won't be
considered to be used as part of equal cost load balancing. So once again, I'd
like to give the
opportunity if you want to launch the lab and do this right now with me. The WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
opportunity if you want to launch the lab and do this right now with me. The
link is near the end
of the skill you can click on it, the lab come up and do that or you can do the
lab at the very end
as well. Either way is great because what we're going to do is we are going to
reset the routing
environment on this topology. So let's do that back at server one. So I
minimize this. There's our
text document. This is server one. So I've got my multi-tap putty here and I've
also got our document
right here and I'm going to go ahead and I'm going to first of all do it with
traditional IPv4. So I'm
going to take the traditional IPv4 implementation of eAGRP. Copy that, copy WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
going to take the traditional IPv4 implementation of eAGRP. Copy that, copy
that and then use the
option we talked about earlier. I'll paste it in there and then I'm going to
apply that to all the
routers and not apply it to the PCs and send it. So effectively that removes
all eAGRP whether it
was named or traditional and it put in traditional eAGRP. So as a spot check if
we did a show IP route
for 8.8.8.8.8. There is our route going through the next top of 242 which is R2
. So right now what WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
. So right now what
that means is that R4 if it wanted to forward traffic down to R8 to 8.8.8.8.8.
It would send it up to R2
and then R2 would make kids routing decision and so on and so forth. Now one
question we might
ask ourselves is why in the world is R4 going to forward a packet if we're
trying to get to 8.8.8.8.8.
Why is it forwarding it this way? Why is that the successor route? So I'll put
it S there for
successor and then we have feasible successors that it's not currently using
going to R3 and then
going down to R6. And I designed this topology with this in mind because I want WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
going down to R6. And I designed this topology with this in mind because I want
you to think about
what is considered as part of the metric calculation for eAGRP. And if you
think back to our earlier
videos it's going to be the sum of delays. So that goes into the calculation
and the lowest
bandwidth in the path. So let's consider for a moment what the default delay is
for gigabit,
the default delay is for Ethernet and then also I artificially specified a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the default delay is for Ethernet and then also I artificially specified a
bandwidth of 64
kilovit per second on all the serial links. So let's go take a look and
identify what those
delays look like from the actual router's perspective. So we can go to R3 and
look at all three of those
right now because R3 has a gigabit Ethernet interface, it has a fast Ethernet
and it has a serial
so let's go to R3. So here on R3 let's do a show interface gig one slash zero,
fantastic. So here
is showing us two things about this interface, the bandwidth which is 1 million WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is showing us two things about this interface, the bandwidth which is 1 million
kilovits per second
and also the delay. So the default delay on a gigabit Ethernet interface is 10
microseconds.
Let's document that. So for the gigabit links it'll be 10 microseconds, great
great great and next
let's take a look at fast Ethernet 4 slash zero. So on R3 we'll do a show
interface for fast Ethernet
4 slash zero and press enter. So here we have our bandwidth which is 100,000
kilovits per second
and this delay is 10 times worse than the gigabit. So the delay is 100 microse WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and this delay is 10 times worse than the gigabit. So the delay is 100 microse
conds. So we'll document
that next. So the fast Ethernet here would be 100 microseconds and 100 here.
And then finally let's
take a look at our serial links at their delay. So on R3 we'll look at serial
interface 3 slash 2
as an example and again on all these serial interfaces I artificially lowered
the bandwidth to 64
kilovits per second which is also going to have an effect on the delay. So if
we do a show interface
serial 3 slash 2 and press enter. So here's the bandwidth that I manually put WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
serial 3 slash 2 and press enter. So here's the bandwidth that I manually put
on all those serial
interfaces and here is the delay. Oh my gosh, 20,000 microseconds. So let's go
document that. So that's
going to be 20K microseconds and the same thing for the serial link right here.
Let's go to 20K
here as well. So for this route to 8.8.8.8 and our four is making its
calculations on what is the
best path based on the composite metric. It's using the sum of the delays as
well as the lowest
bandwidth in the path. So from our fours perspective the lowest bandwidth in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
bandwidth in the path. So from our fours perspective the lowest bandwidth in
the path is always going to be
64K because it's going to have to go through either this serial link or that
serial link to get there
and that's the lowest bandwidth in the path. So that's going to go into the
calculation and then the
other factor is going to be the sum of the delays. So let's go ahead and use a
couple colors. Let's go
ahead and calculate the sum of the delays if our four was going to go here to
here and then our three
could route it down to our 8. So we'll call that path a. So some of the delays
there would be 20,100 WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
there would be 20,100
for the sum there. So that would go into the calculation as we're talking about
these sum of
the delays and let's use another color here for the path from our four going
this direction. So the
delays here would be ethernet would be 100. So here on path B the sum of the
delays would be 20,100
and let's calculate the path that based on the routing table is going to be
using and that's going
this direction. So for path C it'd be 10 for this leg of the journey and 10
more for that leg and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
more for that leg and
then 10 more for there and then it'd be 20,000 here so that'd be 20,000 and 30.
And that's why
router 4 has a lower feasible distance going up through our two is because as
part of its calculation
the sum of the delay is 20,030 versus 20,100 this way going through path a or
20,100 going through path b.
So just to confirm if we go back to our four and we do a show IP eEdGRP top
ology and press enter
we'll go down a few lines we'll stop around the 888 network right here it has WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we'll go down a few lines we'll stop around the 888 network right here it has
one successor
and that feasible distance is this metric right here and that's going through
our two and then we
have two feasible successors where we could use those if the primary route goes
away or if we use
the variance command we can specify that anything that two times are three
times are four times
this current metric. If we have feasible successors within that range they
could also be used and we
can start doing proportional load balancing. Now in this case each of the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
can start doing proportional load balancing. Now in this case each of the
metrics is so close
for the feasible successors that it'd probably be doing equal cost load
balancing but if you
had some links that were like two or three or four times as worse and you set
the variance to like five
if then do proportional load balancing and send more traffic over the much
better paths
and less traffic over the least best paths but because our metrics are so darn
close it's very likely
to do equal cost load balancing because it's just a almost a rounding error
about the metrics
involved here. So currently let me verify which flavor of eEdGRP we just put in WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
involved here. So currently let me verify which flavor of eEdGRP we just put in
we'll do a show
IP protocols. So let's do a show run pipe section router. I think we did
traditional but just to confirm
sure enough and so if we wanted to we could go into router configuration mode
with a config T
I'll just copy paste router eEdGRP 18 in and let's do a quick do show IP route
for 8888. We should have
one specific route that's going through the next top of 10.0.24.2 which is true
. Now check this out
now we can use the variance command and we can say variance for example five WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
now we can use the variance command and we can say variance for example five
and what effectively
that means is that any feasible successors that we have if their metric is not
worse than five times
the current metric or the feasible distance for the successor route go ahead
and also use them.
Now in our case they're all super close so we could do a variance of two and
what that would mean
is that any feasible successors that have a metric that's not greater than two
times the current
feasible distance that's the metric for the winning route they can be used for
load balancing. So
let's go ahead and do variance two. Let's do a do show IP route in fact I can WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
let's go ahead and do variance two. Let's do a do show IP route in fact I can
hit the upper
acute few times for that. Well the do show route in fact I can hit the upper
acute a couple times
for that. Let's do a do show IP route for 8888 and check this out. Now we have
this route 10.0.24.2
is the next top but we also have the next top of 10.0.34.3 and 10.2.46.6 and
also because the metrics
are so close check this out. We have that metric versus that metric. No no
store even those are
feasible successors and then we have this metric for what was the successor WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
feasible successors and then we have this metric for what was the successor
route because they're so
darn close it's showing the traffic share count for this route is one and one
for that and one for
that where if we had significantly different metrics and we use the variance
command the routes that
did qualify and they did get the routing table they would have a traffic count
that's higher for
the preferred route and a lower traffic share count for the less preferred
routes based on the
metrics. So also right here if we did a show IP route and we get down to 8888
so we'll be down a
page or two here. There we go. Now in our routing table we have three routes WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
page or two here. There we go. Now in our routing table we have three routes
that we can load balance
across. And if we did a show IP edg rp topology and pressed enter check this
out for you down to
8888 network. It's now showing that we have three successors three winners that
all got in and
that's because we set up the variance of two and just as a verification of that
video show run
section router we can verify that as well. So there's our variance command and
if we remove that
for example let's go ahead and go into router edg rp 18 and we said no variance WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
for example let's go ahead and go into router edg rp 18 and we said no variance
and then we do do show
IP edg rp topology and go down to 8888 network you'll notice that we now only
can have one successor
route and the other two are feasible successors. Then we put it back with
variance two so now we do
variance two and we look at the IP edg rp topology table once again for that 8
888 network we now have
three successors. We could also verify that with a trace. So if we did a trace
down in fact let's just
do it long hand with a trace route IP going to 8888 and let's go ahead and use WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
do it long hand with a trace route IP going to 8888 and let's go ahead and use
this default source
address and we'll press enter a few times and then for the probe count let's go
ahead and do
let's do 10 for each probe press enter a few times let that run check this out
for the first
top let's bring up our topology real quick. For the first top as r4 is doing a
trace to 8888 it's
using 10 0242 and then for the second one 10 0343 that's r3 and for the third
one 10246 and this
doing a round robin once again for two three and six two three and six and then WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
doing a round robin once again for two three and six two three and six and then
for the second
hop in the path that would be depending on the routing tables for r2 and r3 and
r6 respectively.
So that's another quick way to verify that the behavior that we're expecting
with load balancing
with eagrp is happening as expected. Now I also want to show you the other
option that's using variants
in the world of named eagrp so if we grab the notepad document again and we go
to the section we're
going to remove all of our current routing and we're going to use the address
families I'll go down
right here we'll copy that and I'm going to plug this into all eight routers
once again so we'll WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
go to the option here we'll go to the type your script section click there
paste it in send that
to all of our devices except for our PCs and then click on send script and that
will remove any
current routing that we have and it will then set up named eagrp so I can
demonstrate how to do
variants inside named eagrp and so the option for that is to go into your eagrp
named configuration
go into the address family for ib-4 then you go into topology base and then
into topology base you
save variants too so I'm going to take that and I'm going to go ahead and put WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
save variants too so I'm going to take that and I'm going to go ahead and put
that on actually I don't
need all routers I see it on r4 for demo so I'm going to grab this and just put
these commands here
on r4 so I'll right click copy that and then here on r4 let's do a show ip
route and take a look at
8888 we have one specific route that's going through r2 again but once we go
ahead and I just highlighted
that so I need to go back and copy again so I'm going to copy that from notepad
paste it into r4
another variants is to check this out now if we do a show ip route and we go
down a little bit now WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
down a little bit now
for the 8888 network we now have three routes in our routing table going
through r6 our three and
our two as next tops and let me show this syntax for that once again with this
show run section
router and press center give that a moment to process and there's the
configuration so inside the
address family for ipv4 we go into topology base and then use your variants
command right there as
opposed to traditional eagrp where you just do it simply in eagrp configuration
mode and then for
verification if you do a show ip protocols here's the eagrp atom system that's WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
verification if you do a show ip protocols here's the eagrp atom system that's
running 100 and
right here we have the variance specified as to because we configured it that
way which allows us
to take feasible successors and as long as their metric doesn't exceed twice
the metric of the
successor route they could also be used in the routing table so up to this
point we've had some
fun and taking a look at the behaviors and characteristics of eagrp and what it
's using to calculate a
metric and decide on which route goes or which routes go into the routing table
and up to this point
you've had a few options you could have clicked the lab to join me and go WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
you've had a few options you could have clicked the lab to join me and go
through a step by step or
if you've waited and want to do it now in the next video i'd like to put you on
a hands-on lab so
if you've already done the work that's fantastic however if you haven't done
the hands-on lab yet
here for eagrp in the next video i'd like to present you with some lab tasks so
you my friend can get
hands-on practice in working with and verifying eagrp so i'll see you in the
next video in just a moment