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Q&A: For Cisco GRE Tunnels, what do high RxLoad and TxLoad values mean?

Question

  • For Cisco GRE Tunnels, what do high RxLoad and TxLoad values mean? 
    • Sometimes customers with Cisco Customer Premise Equipment (CPE) look at their tunnel interfaces, and notice the "RxLoad" and "TxLoad" values are high, and wonder what it means.
      • Example:
      • xxxxxxxxx#sh int Tunnel0
        Tunnel0 is up, line protocol is up
        Hardware is Tunnel
        Description: Silverline
        Internet address is X.X.X.X/30
        MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec,reliability 255/255, txload 1/255, rxload 239/255 Encapsulation TUNNEL, loopback not set
        Keepalive set (30 sec), retries 3
        Tunnel source X.X.X.X, destination X.X.X.X
        Tunnel protocol/transport GRE/IP
        Key disabled, sequencing disabled
        Checksumming of packets disabled
        Tunnel TTL 255, Fast tunneling enabled
        Tunnel transport MTU 1476 bytes
        Tunnel transmit bandwidth 8000 (kbps)
        Tunnel receive bandwidth 8000 (kbps)
        Last input 00:00:13, output 00:00:05, output hang never
      • Notice the txload/rxload in green. The RxLoad is showing 239/255.

Environment

  • Silverline DDoS
  • Cisco
  • GRE Tunnels
  • BGP Routing

Answer

  • RxLoad is a value determined by the bandwidth set on the router's interface.
    • If it's not set manually, it tends to either inherit from the parent interface, or go with a low default.
    • From the "show interface" output above, note the red section, where the interface is configured for "BW 100 Kbit/sec" which corresponds to less than 1Mbit.
  • If you issue a correct "bandwidth" statement in the routers interface configuration, the tx/rxload #'s will reflect the actual interface speeds.
  • 10Mbit : BW 10000
    100Mbit : BW 100000
    1gigabit: BW 1000000
    10gigabit : BW 10000000

     

    ****

    my.router#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    my.router(config)#int tunnel 1
    my.router(config-if)#bandwidth 10000
    my.router(config-if)#end

    ****

  • Now the RXLoad value will be calculated on percentages of 100Mbit.

 

 

 

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