Q&A: For Cisco GRE Tunnels, what do high RxLoad and TxLoad values mean? – F5 Silverline Knowledge Base

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.