On 9/17/15, Soumit <soumit.s...@gmail.com> wrote: > Have you got packet captures for SNMP requests. Even if jumbo frames > enabled does the SNMP datagrams are really that big (>1500)
The problem with enabling jumbo frames (ie. MTU > 1500) is that _every_ device on the subnet, including routers & switches, has to be configured with the same MTU size or else you will drop some traffic. On the other hand, as long as you don't have stupid firewall rules like 'drop non-initial fragments', large packets work just fine. If you can get access to a Cisco switch, see for yourself: on the switch: conf term snmp-server community foo ro snmp-server packetsize 9000 end on the workstation, start capturing packets & do: snmpbulkwalk -c foo -Cr100 ipAddressOfSwitch .1.3.6 If you're using wireshark you'll see lots of instances that look like Fragmented IP protocol (proto=UDP 17, off=0, ID=0251) [Reassembled in ... Fragmented IP protocol (proto=UDP 17, off=1480, ID=0251) [Reassembled in ... Fragmented IP protocol (proto=UDP 17, off=2960, ID=0251) [Reassembled in ... Fragmented IP protocol (proto=UDP 17, off=4440, ID=0251) [Reassembled in ... Fragmented IP protocol (proto=UDP 17, off=5920, ID=0251) [Reassembled in ... get-response Regards, Lee > On 16 Sep 2015 20:38, "Lee" <ler...@gmail.com> wrote: > >> On 9/16/15, AR, Giridhar <giridhar.raja...@netapp.com> wrote: >> > Hi Lee, >> > >> > Thanks for the response. >> > No I didn't change the MTU on every router and switches between client >> and >> > server. >> > >> >>What is the relation between MTU and max_repetitions.? >> >> If we change the MTU to jumbo frame like 9000, what should be these >> >> macros (SNMP_MAX_MSG_SIZE , SNMP_MAX_LEN ) should be set ? >> >> Is there any other changes in need to perform? >> > >> > Do you have any inputs on the above questions? >> >> Don't change the MTU. If you do, and don't change the MTU on your >> routers & switches, anything you send > 1500 bytes will be dropped. >> >> I'm not exactly sure what you're trying to accomplish, but if I was >> trying to change how much info could be returned I'd start with >> changing SNMP_MAX_MSG_SIZE and see if that worked. >> >> Regards, >> Lee >> > >> > Thanks >> > Giridhar >> > >> > -----Original Message----- >> > From: Lee [mailto:ler...@gmail.com] >> > Sent: Wednesday, September 16, 2015 5:13 PM >> > To: AR, Giridhar >> > Cc: net-snmp-coders@lists.sourceforge.net >> > Subject: Re: guidelines to increase the MTU size >> > >> > On 9/16/15, AR, Giridhar <giridhar.raja...@netapp.com> wrote: >> >> Hi >> >> >> >> Need guidelines to increase the MTU size (example from 1500 to 9000) >> >> Our application is using snmpv2. When the MTU size (9000) is changed >> >> on interface of client and server, Snmp queries are timed out. >> > >> > Did you also change the MTU on every router & switch between the client >> and >> > server to be 9000? If no, that's probably why queries are timing out >> > >> > Regards, >> > Lee >> > >> > >> >> We collected the packet traces on both client and server. Client is >> >> receiving the response from server, but client is dropping the packet. >> >> Following are the test cases tried >> >> >> >> case client MTU server MTU >> >> result >> >> >> >> 1 1500 1500 >> >> passed >> >> >> >> 2 1500 9000 >> >> failed >> >> >> >> 3 9000 1500 >> >> passed >> >> >> >> 4 9000 9000 >> >> failed >> >> >> >> >> >> Looked at the client code, uses the net-snmp-code, >> >> >> >> >> >> >> >> #define SNMP_MAX_MSG_SIZE 1472 >> >> #define SNMP_MAX_LEN 1500 >> >> >> >> And by default max_repetitions is set 20. If we set to 1, snmp queries >> >> are successful. >> >> >> >> What is the relation between MTU and max_repetitions.? >> >> If we change the MTU to jumbo frame like 9000, what should be these >> >> macros (SNMP_MAX_MSG_SIZE , SNMP_MAX_LEN ) should be set ? >> >> Is there any other changes in need to perform? >> >> >> >> >> >> Thanks >> >> Giridhar >> >> >> >> >> >> >> >> >> >> >> >> >> > >> >> >> ------------------------------------------------------------------------------ >> Monitor Your Dynamic Infrastructure at Any Scale With Datadog! >> Get real-time metrics from all of your servers, apps and tools >> in one place. >> SourceForge users - Click here to start your Free Trial of Datadog now! >> http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 >> _______________________________________________ >> Net-snmp-coders mailing list >> Net-snmp-coders@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/net-snmp-coders >> > ------------------------------------------------------------------------------ _______________________________________________ Net-snmp-coders mailing list Net-snmp-coders@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/net-snmp-coders
