IP SLA on 2950s

Is not supported!

2950(config)#ip s?
security  source-route  sticky-arp  subnet-zero

Instead, to configure two 2950s as IP SLA responders, configure them as rtr responders. 
The RTR stands for Response Time Reporter and more information can be found here: http://www.cisco.com/en/US/docs/ios/12_0t/12_0t3/feature/guide/RTRenh.html

If you’re working on the CCNP Switch Lab: IP Service Level Agreements in a Campus Environment; for Step 9: Configure Cisco IOS IP SLA responders:

Instead of using:

ALS1(config)# ip sla responder
ALS2(config)# ip sla responder 
ALS1(config)# ip sla responder udp-echo ipaddress 172.16.1.1 port 5000
ALS2(config)# ip sla responder udp-echo ipaddress 172.16.1.1 port 5000

USE:

ALS1(config)# rtr responder
ALS2(config)# rtr responder
ALS1(config)# rtr responder type udpecho ipaddress 172.16.1.1 port 5000
ALS2(config)# rtr responder type udpecho ipaddress 172.16.1.1 port 5000

SLA Show:

DLS1#show ip sla ?

  application             IP SLAs Application
  authentication          IP SLAs Authentication Information
  configuration           IP SLAs Configuration
  enhanced-history        IP SLAs Enhanced History
  group                   IP SLAs Group Scheduling/Configuration
  history                 IP SLAs History
  reaction-configuration  IP SLAs Reaction Configuration
  reaction-trigger        IP SLAs Reaction Trigger
  responder               IP SLAs Responder Information
  statistics              IP SLAs Statistics 

RTR Show:

ALS1#show rtr ?
  application               RTR Application
  authentication            RTR Authentication Information
  collection-statistics     RTR Statistic Collections
  configuration             RTR Configuration
  distributions-statistics  RTR Statistic Distributions
  history                   RTR History
  operational-state         RTR Operational State
  reaction-trigger          RTR Reaction Trigger
  responder                 RTR Responder Information
  totals-statistics         RTR Statistics Totals

ALS1#show rtr responder
RTR Responder is: Enabled
Number of control messages received: 120 Number of errors: 0
Recent sources:
        172.16.1.1 [05:01:11.318 UTC Mon Mar 1 1993]
        172.16.1.1 [05:00:11.318 UTC Mon Mar 1 1993]
        172.16.1.1 [04:59:11.318 UTC Mon Mar 1 1993]                  
        172.16.1.1 [04:58:11.314 UTC Mon Mar 1 1993]
        172.16.1.1 [04:57:11.310 UTC Mon Mar 1 1993]
Recent error sources:

udpEcho Responder:
  IP Address             Port
  172.16.1.1             5000

Cheers!