Troubleshoting packet flow on 6500 and unicast routing

Toubleshooting flow chart to use during unicast troubleshooting.


                            Start
                                |
                               V 
   
 Route programming in software and hardware

  Show ip route  (In software)
  Show mls cef exact route (In hardware)
                                |
                               V

 ARP programming in software and hardware

 Show ip arp (In software for next hop -address given in show ip route)
 Show mls cef adjacency (In hardware for next-hop address given in show ip route)
                                |
                               V

Mac programming in software and hardware

Show mac-address address <>  (mac address given in show ip arp for next-hop address )

remote command switch Show mac-address address <>  (mac address given in show ip arp for next-hop address )
                                |    
                               V
  
Spanning tree programming in software and hardware

Show spanning-tree  vlan <> (In software)
remote command switch show table (In hardware)

                                |    
                               V

Default acl programming in hardware

Show tcam interface gigabitEthernet <> acl in ip detail all1
                                |    
                               V

 LTL (interface) programming in hardware
                                |    
                               V

 Error counters on the interfaces involved

 Show interface gigbitethernet <> counters (In software)
 Show interface gigbitethernet <> counters error (In software)
 Show counters interface gigabitethernet <> (In software)

                                |    
                               V


Error register dump of the ASIC's involved in the path from CPU to interface
                                |    
                               V


Packet captures (ELAM)
                                |      
                               V
                             End

QOS Troubleshooting on 6500/3750/2900/4500

DSCP TOS CoS Precedence conversion


Need to be updated.


QOS on 4500


Show platform hardware qos interface<> tx-queue

show policy-map interface <>



QOS on SUP720


show mls qos int gig <> statistics    -------->  Does not work on SUP720 .

ip access-group on layer 2    ------->    Does not work on SUP720 trunk interface as well.



QOS on SUP2T


By default ,its trust DSCP , Checked and verified in the lab with SUP2T.

Port QOS is disabled on interface if "auto qos default " disabled.

Show queueing interface teng1//1  or gig interface on SUP2T




QOS on 2960/3750

 Show mls qos int gig1/0 statistics--------> To check the incoming/outgoing dscp marking and drops and enqued

Show mls qos queuse-set 1 or 2

clear mls qos interface gig1/0 statiscts-----> To clear the mls qos statistics used this command.


mls qos queueu-set output 1 buffer  5 10 80 5

mls qos queueuset- threshold 100 100 100 400 ……….>   Two ways to give more buffer 1) assign buffers from others queue or move the  the threshold  to correct level or increase reserved threshold value  or increase the maximum percentage and then adjust the threshold value

make sure to check cos and dscp queue for correct  threshold mapping .

DHCP Troubleshooting

Show ip dhcp snooping statistics details ---------> To check the dhcp snooping packet drops.

To enable the DHCP relay on switch in a vlan by following below command.


service dhcp

ip helper-address 1.1.1.1 ------- To enable  DHCP relay on 6500 switch under SVI. Define DHCP server ip address.



Below are the flowchart of DHCP server /client packets during troubleshooting.



DHCP Discover (TX123456) ----------->PC sends DHCP discover to broadcast for the DHCP ip address
       |
      V
DHCP offer  (TX123456)----------------->Reply from DHCP server with client ip address
      |
     V
DHCP request  (TX123456) ----------->  DHCP client send again request with allocated ip address
      |
     V
 DHCP Acknowledgement  TX123456)   ----------->Acknowdgement received from DHCP server.
      |
     V
DHCP inform   -----------> DHCP informa is used if PC/client needs additional information like option 66 and option 67.
      |
     V
DHCP Acknowledgment.  -------> DHCP server acknowledge to inform packet by using DHCP ack to client with option 66 and option 67.


Debugging command to use when DHCP relay agent is in use

debug ip dhcp server packet

Not working logs:  

Aug 16 14:24:03.919 EDTT DHCPD: setting giaddr to 10.1.1.1.
Aug 16 14:24:03.919 EDTT DHCPD: BOOTREQUEST from 0178.acca.b2d3.f2 forwarded to 10.10.10.10.
Aug 16 14:24:03.923 EDTT DHCPD: BOOTREQUEST from 0178.acca.b2d3.f2 forwarded to 10.10.10.20.
Aug 16 14:24:04.731 EDTT DHCPD: setting giaddr to 10.1.1.1.
Aug 16 14:24:04.731 EDTT DHCPD: BOOTREQUEST from 01d4.8561.b441.4d forwarded to 10.10.10.10.
Aug 16 14:24:04.735 EDTT DHCPD: BOOTREQUEST from 01d4.8561.b441.4d forwarded to 10.10.10.20
Aug 16 14:24:05.263 EDTT DHCPD: setting giaddr to 10.1.1.1.

 
Working logs:

Aug 17 01:23:17.899 EDTT DHCPD: setting giaddr to 1.1.1.1.
Aug 17 01:23:17.899 EDTT DHCPD: BOOTREQUEST from 0111.1114.1b16.c1 forwarded to 10.10.10.10.
Aug 17 01:23:17.899 EDTT DHCPD: BOOTREQUEST from 0111.1114.1b16.c1 forwarded to 10.10.10.20.
Aug 17 01:23:18.163 EDTT DHCPD: forwarding BOOTREPLY to client 0022.2233.1223.
Aug 17 01:23:18.163 EDTT DHCPD: Forwarding reply on numbered intf
Aug 17 01:23:18.163 EDTT DHCPD: creating ARP entry (10.11.11.11, 0022.2233.1223).
Aug 17 01:23:18.163 EDTT DHCPD: unicasting BOOTREPLY to client 0022.2233.1223 (10.11.11.11).
Aug 17 01:23:18.167 EDTT DHCPD: setting giaddr to 10.1.1.1.

debug ip dhcp snooping packet mac <client mac address>



 Not working logs:
 DHCP_SNOOPING: process new DHCP packet, message type: DHCPDISCOVER, input interface:

Working logs: 

 DHCP_SNOOPING: process new DHCP packet, message type: DHCPDISCOVER, input interface:

DHCP_SNOOPING: process new DHCP packet, message type: DHCPOFFER,