Request Time Out / Packet Drops

[Nagaraju Chengeli]

Hi There,

I have four Sites A,B,C,D which are connected through Point-to-Point links.

Each site has 3750 switches where the P2P links are terminated.

We have enabled EIGRP protocol for routing.

I have 10 access layer(2960) switches terminated on 3750 on each sites.

Note: Each site has service provider MUX installed from where we take an link towards to 3750 port and each link has 40 Mbps bandwidth.

Questions:

1) When we do a continues ping from Site-A to Site-B we observed request time outs.

2) Out of 2000 request we found 8 packets.

3) Do we need to worry about this if you have a high production support which run's 24x7 which mostly depends on voice  and data.

4) Why do we get request time outs in LAN traffic and if so how do i stop it.

5) How can i maintain a constant Latency across the sites.

6) How can i make my network on each site to ensure there no packet drops on LAN and WAN.

7) We found that one of a host causing flooding in the networking using firewall but what kind of configuration do i need to do on access switch so that if my switch identifies flooding by host and stops it on port level before spreads on network.

Thanks

NagarajChengeli

[Richard Bradfield]

Let me understand this,

your P2P links terminate on a Catalyst 3750 switch, you do not have a router as such.

re your question 2) are you saying you only drop 8 packets out of 2000? 

3) if  you have voice and Data have you setup QOS on the switches?

4) ICMP traffic will be set as low priority if QOS setup  so in busy times might get dropped. Do the service provider Muxes recognise DSCP or COS markings

5) setup proper QOS better if had a router between the sites, can set a better QOS policy with routers.

6) you are always going to get some packet drop across a busy WAN connection

7) you can put storm on control on interfaces this might help.

HTH

Richard.

[Nagaraju Chengeli]

Hi Richard,

1) Yes i don't have router in my network as we are using 3750 for routing.

2) Yes that is only on a particular time we found that out of 2000 ICMP requests we found 8 packet dropped but that varies  each time you do ICMP test.

3) Yes i have enabled MLS QoS globally on all 3750 switches and made all my up-links and Access layer switches to trust DSCP marking across the sites.

4) Is it required to configure service provider MUX to trust DSCP because as per the conversation with ISP they said there is no configuration required on their END as the MUX transfer the signal with our priorities. 

i) why do we get request time outs in local LAN as they are 1Gbps port.

5) i)As 3750 has routing capabilities and QoS enable can i do better QoS policies.

ii) what are all the limitations it has with routing and other features.

iii) And setting a best QoS polices will ensure to have a constant latency.

6) So you mean to say i dont need to worry if my wan link is busy.

i) what if my wan link is not totally utilized and i'm still getting packet drops.

Thanks

Nagaraj

[Richard Bradfield]

Hi Nagaraj,

see link below for configuring inbound policy maps on the 3750s and other QOS features

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91862-cat3750-qos-config.html

it is better to have policy maps on the outbound interfaces, and this can be done by a router.

As a matter of interest do you have any problems with the voice traffic?

regards

Richard.

[Nagaraju Chengeli]

Yes Richard i have configured QoS on access layer and L3 3750

i have a call center with 100 agents where they use X-Lite soft phone for voice call which is an open source.

i made voice traffic to mark with DSCP 46 and 26 using windows group policy.

after that i made access layer ports to trust DSCP marking.

then i made all the uplinks and wan interfaces to trust DSCP marking by giving # mls qos trust DSCP command on interface.

i made the WAN link outbound interface to trust DSCP is it not enough do i need to write policy maps to trust my DSCP traffic.

Thanks

Nagaraj

[Richard Bradfield]

I take it the voice quality is not that good, do customers complain? what codec tdo the voice calls use? is it g711 or g729?, Is it mainly voice traffic across the WAN links?

Please see the policy-map section in the link I previously posted, this details what you need to do. Here it is again.

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/91862-cat3750-qos-config.html

[Joseph W. Doherty]

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Posting

1) When we do a continues ping from Site-A to Site-B we observed request time outs.

What's the question?

2) Out of 2000 request we found 8 packets.

What's the question?

3) Do we need to worry about this if you have a high production support which run's 24x7 which mostly depends on voice  and data.

Probably, especially as you mention you're also supporting voice.

4) Why do we get request time outs in LAN traffic and if so how do i stop it.

There are many possible reasons.  First you would need to figure out what are the reasons are for your timeouts (could be multiple).  Then, you would need to determine whether they can or should be mitigated.

5) How can i maintain a constant Latency across the sites.

Well, insuring there's more available bandwidth than will ever be used.  Often difficult to do for all network traffic.  Also often can be done for some network traffic.  (E.g. you might insure there's always sufficient bandwidth for Voice traffic.)

6) How can i make my network on each site to ensure there no packet drops on LAN and WAN.

Again, by insuring you always have available bandwidth.

7) We found that one of a host causing flooding in the networking using firewall but what kind of configuration do i need to do on access switch so that if my switch identifies flooding by host and stops it on port level before spreads on network.

What kind of "flooding"?