Measuring bandwidth using IP SLA

[sir_ulrick]

Hi, 

I would like to understand how works ip sla to measure bandwidth. I have reading in this community and it's recommended to use udp jitter and udp echo values to take a measure of bandwidth using a MPLS but I have some questions:

1) These are trustworthy values? What happen with TCP traffic or if Im not using a MPLS line?

2) I suppose that I would have to configure a ips sla with these values (jitter and echo udp) every X seconds? Is it correct? Would be possible to produce a network congestion for this reasons?

3) I'm not going to use a monitor system or SMNP, only I would like to use ip sla to send bandwidth capabilities to different device to check theses values (threshold). Is it possible or I need SNMP? Could generate any problem with this configuration?

Thanks in advance!

[Spooster IT Services]

Hi Ulrick,

Please find my answer inline below:

1) These are trustworthy values? What happens with TCP traffic or if I'm not using an MPLS line?

Yes, these values are trustworthy and monitoring a sort of real-time performance of your circuits. For TCP connections monitoring, you can use TCP-connect but for TCP Jitter, delay hardly matters as  TCP relies on successful transmission of packets.

2) I suppose that I would have to configure an IP SLA with these values (jitter and echo UDP) every X seconds? Is it correct? Would be possible to produce network congestion for these reasons?

Yes, you need to configure IP SLA with these values. I don't think SLA will not cause any network congestions.

3) I'm not going to use a monitor system or SMNP, only I would like to use IP SLA to send bandwidth capabilities to different devices to check theses values (threshold). Is it possible or I need SNMP? Could generate any problem with this configuration?

SNMP will provide you centralized monitoring of all your sites. If you are not planning to use SNMP then you need to go to all the devices one by one to check these values. This would not generate any problem with configuration. 

You will find all the information regarding IP SLA on the link below:

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipsla/configuration/15-mt/sla-15-mt-book/sla_overview-0.html

Please give a thumbs up if you find my answer as useful.

[sir_ulrick]

Thanks a lot for your quick reply! You really helped me! but after reading your docummentation I have new questions:

1) How exactly I can measure bandwidth with jitter / rtt? I suppose that I need to talk with ISP to check minimum theorical bandwith. For example, my ISP tell me that jitter between node A and B is 100 ms, if I have a jitter of 120 ms that means that I have about 20% of my bandwidth? how jitter and bandwidth are related exactly?

2) If I have any ECMP protocol and I'm ussing different interface, how will work ip sla? I would have 3 different interfaces working simulteasnily to reach destine node, for example, with one IP SLA probe. What exactly will it measure?

Thanks in advance

[Joseph W. Doherty]

#1 jitter and/or rtt alone do not, cannot, measure bandwidth. Jitter and bandwidth are generally not related.

#2 Generally, ECMP will send a "flow" on one path, so what a probe would measure is the performance of that one path. Depending how ECMP chooses path, multiple measurements might be sent on just one path, or different paths for each probe.

[sir_ulrick]

1) So why it use udp-jitter and udp-echo (please see my link on mi first message) to measure the bandwidth? How is it possible to measure bandwidth with ip sla?

2) But ECMP precisely works using all best paths (different interfaces) to reach destination, so I suppose that it will use different paths.How will this affect to the probe?

[Joseph W. Doherty]

#1 I hadn't early followed and read the linked referenced posts, but just did. I didn't notice anything in the posts noting you could use jitter and/or echo test to measure bandwidth. Could you point that out to me?

I don't recall if Cisco's SLA tests provide one for measuring bandwidth although I have a hazy recollection there might be one in newer/some SLA feature sets. (I recall a new feature [couple years back] that could dynamically adjust a tunnel's shaper to available bandwidth - using some form of SLA[?]. [In theory, you mightcompute bandwidth receiving two packets that you know were sent as an immediate pair.])

#2 Again, if a probe is seen as one flow, you'll get results for one of the paths selected (although might be difficult to determine which was actually used). If a probe is seen a multiple flow, then parts of it might be directed across multiple path and you get a result based on how the packets actually traveled, which again might not give you an easy way to determine what's happening.

In the real world, with ECMP, using SLA to notify you it's "seeing" some performance issue even if it doesn't make it easy to identify which of a ECMP path is the problem could still be useful.

[sir_ulrick]

Hi, 

in the my first message link (https://community.cisco.com/t5/routing/ip-sla-bandwidth-monitor-and-packet-loss/td-p/3697308) it suggested to use udp-jitter and udp-echo. My question is, how it is possible to measure bandwidth to monitoring, for example, of our ISP? Usually, companies using IPSLA to management these values.

[Joseph W. Doherty]

Ok, again, jitter and/or echo test generally cannot monitor bandwidth.

[sir_ulrick]

Thanks for your reply Joseph, if I cann't use these values to measure bandwidth how can I measure and evaluate my link status with my ISP? I mean, using different monitoring tool, for example, solarwind. I think it's necessary to determine some theorycal basics values and then check increasing of these values

[Joseph W. Doherty]

If you're trying to verify your ISP's bandwidth provided, there are quite a few public tools with servers on the Internet that will provide an up and down bandwidth measurement. Try one of those.

If you're looking to verify bandwidth between two (or more) of Internet connected sites, there are public tools, you can install on Windows or Unix system to measure bandwidth between a pair of hosts.

For on-going monitoring, something like Solorwinds, or its like, might have a bandwidth test you can "schedule" and graph.

[sir_ulrick]

Thanks again for your help, but I can't use any windows or unix server. Only I can use cisco devices, for this reason I'm investigating about IP SLA values to measure ISP bandwidth

[Joseph W. Doherty]

Years ago, some Cisco devices had a "hidden" ttcp command. You might try to see if yours do, although most likely not.

[sir_ulrick]

Thanks Joseph!!!