Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Community Member

how do i measure packet loss?

Hello,

How do i measure packet loss on a point to point ethernet wan link using cisco routers?

Does it depend on the datagram size?

1 ACCEPTED SOLUTION

Accepted Solutions

Re: how do i measure packet loss?

HI, [Pls Rate if Helps]

Thanks for Posting the Configuration.

I see in R2 FEth 1.50 you have 3-IP's assigned. 1-Primary & 2-Secondary IP.

Since R1----R2 are directly connected. I hope the error is with IP Assignments.

Required, a Static Route from R1----R2 for the same Subnet "255.255.255.252" . Since the IP's assigned (Pri & Sec) to FastEth1.50 is in different Subnet the R1 is taking time for locating the correct IP Subnet.

Else, do a Test by removing all the Sec..IP & assign "255.255.255.252" Subnet as Pri..IP for the Sub-Interface FEth 1.50

Also, in R1 under FEth0 set the "encapsulation to dot1Q 50"

Hope this Helps you. Pls Rate if Helps

Best Regards,

Guru Prasad R

10 REPLIES

Re: how do i measure packet loss?

Hi,

You should do multiple extended pings, increasing the datagram size and monitoring the packet loss percentage, as some links will have huge packet loss percentage with a higher packet size rather than low packet size.

HTH,

Mohammed Mahmoud.

Community Member

Re: how do i measure packet loss?

Hello,

I've noticed when i do extended pings sending let's say 200 packets with 100 bytes datagram size ( which is the default) i have 3% packet loss.

when i do extended pings with datagram size 1500 (ethernet maximum size), sending 20 packets i get 25 % packet loss :((

What datagram size should i use and how many packets to send?

What are normal values?

Please help!

Re: how do i measure packet loss?

Hi, [Pls Rate if Helps]

Do Extended Ping between End - to - End Interface of the Devices.

3% of Loss with Default Size of Datagram means then it should be a Service Provider Issue, Line Commisioning Issue, etc.,

Pls Check Do you have any CRC & Input Errors in the Interface.

If any means do "clear counters" & monitor for few Hrs if the errors increases again.

25% of Loss with 1500 Datagram size means before doing this test Pls check if there is any MTU size defined for the Interface.

Also, You can send any number of Packets (ie., more than 1000 even) & datagram size can be default / even depends on the Capability of the Interface type (Eth, Serial, FastEth) / even depends upon the MTU definition on the Interface.

Pls Rate If Helps

Best Regards,

Guru Prasad R

Community Member

Re: how do i measure packet loss?

Hi guruprasadr

Thank you very much for your reply.

The end to end interfaces are Fastethernet.

There are 0 CRC & Input Errors on both end to end interfaces.

The other device's interface ( fastethernet 1) is configured with subinterfaces with encapsulation dot1q, and the subinterface which is connected to me is configured with secondary addresses.That subinterface has MTU 1500 bytes and my fastethernet has also 1500 bytes.

My router's fastethernet is configured normally with just one ip address ( no subinterfaces or secondary addresses)

Something which is very weird: When i ping from my laptop (with windows xp) like this:

ping x.x.x.x -l 1500 -t i don't see any packet loss and everything is ok.

When i ping from the router i get packet loss.

Do you think it has something to do with the encapsulation defined on the other router's fast ethernet?

If you want to know more details, please ask and i will reply asap.

Thanks again for your help

Re: how do i measure packet loss?

HI, [Pls Rate if Helps]

Both the end - to - end Interface should have same Encapsulation, Speed, Duplex Settings.

Mismatch of above is also a Major reason for packet Loss in the Link.

Pls Check & redo the required Configuration.

PLS Rate If Helps

Best Regards,

Guru Prasad R

Community Member

Re: how do i measure packet loss?

ok, but when i ping from my laptop ( which is connected to the router) i don't get any packet loss, but when i ping from the router to the other router i have packet loss.

Regarding encapsulation how do i set encapsulation on my fasteth interface, because this is just normal interface, i don't have subinterfaces, trunks or anything like this.

Re: how do i measure packet loss?

HI, [Pls Rate if Helps]

Try to do "Extended Traceroute" to the destination from Laptop & Router.

Check what is the Gateway of the Laptop. Is that taking the same GW of the FastEth you are using....

Verify the Routing Path (to destination) is same for both the Trace results.

Laptop - to - Destination

Router - to - Destination

Note:Whether the Destination is same IP Address / Different

Again, Check the Routing Path / Gateway of both the Laptop & Router Interface in Source Side....

reg: Encapsulation:example:

-------------------

interface fastethernet1/1.100

encapsulation dot1q vlan-identifier

Pls RATE if Helps

Best Regards,

Guru Prasad R

Community Member

Re: how do i measure packet loss?

Hi,

The two routers are directly connected via ethernet. The ISP made a layer 2 VLAN for us.

Between the two routers we have a /30 subnet.

The topoly is like this:

Laptop---R1---R2---internet

Config on R1's fast ethernet:

interface FastEthernet0

ip address x.x.x.x 255.255.255.252

ip verify unicast reverse-path

no ip redirects

no ip proxy-arp

ip nbar protocol-discovery

ip nat outside

ip virtual-reassembly

duplex auto

speed auto

Config on R2's fastethernet:

interface FastEthernet1

no ip address

no ip redirects

load-interval 30

duplex auto

speed auto

interface FastEthernet1.50

encapsulation dot1Q 50

ip address t.t.t.t 255.255.255.248 secondary

ip address x.x.x.x+1 255.255.255.252 secondary

ip address j.j.j.j 255.255.255.248

ip nat inside

ip virtual-reassembly

no snmp trap link-status

no cdp enable

interface FastEthernet1.75

encapsulation dot1Q 75

ip address v.v.v.v 255.255.255.252

ip nat inside

ip virtual-reassembly

no snmp trap link-status

no cdp enable

So, fa0 on R1 is directly connected with fa1 on R2

Re: how do i measure packet loss?

HI, [Pls Rate if Helps]

Thanks for Posting the Configuration.

I see in R2 FEth 1.50 you have 3-IP's assigned. 1-Primary & 2-Secondary IP.

Since R1----R2 are directly connected. I hope the error is with IP Assignments.

Required, a Static Route from R1----R2 for the same Subnet "255.255.255.252" . Since the IP's assigned (Pri & Sec) to FastEth1.50 is in different Subnet the R1 is taking time for locating the correct IP Subnet.

Else, do a Test by removing all the Sec..IP & assign "255.255.255.252" Subnet as Pri..IP for the Sub-Interface FEth 1.50

Also, in R1 under FEth0 set the "encapsulation to dot1Q 50"

Hope this Helps you. Pls Rate if Helps

Best Regards,

Guru Prasad R

Community Member

Re: how do i measure packet loss?

Hi

Thank you very much for your reply.

Your replies are very good and i learned a lot from them.

Unfortunately i can not do the tests you said because R2 is connected to other sites and there is no error with ip assignments , because the config on R2 was done by somebody else.

I will set the encaps on faeth0 and see what happens.

Thank you again for your time.

Best regards,

O.

2711
Views
5
Helpful
10
Replies
CreatePlease to create content