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Jeffrey Simon

Low Bandwidth Over WAN Interface

I have Verizon FIOS 150/65 service.  I recently upgraded my router from the stock Actiontec router provided by Verizon to a Cisco 3845.  After the upgrade my up and down speeds are peaking at about 55Mbit/second.  Prior to installing the 3845 I was maxing out the service with full 150/65 with sustained speed tests.  I tried another Cisco router as well and I am getting the same results.  As soon as I go back to the Actiontec the speed increases again.  I did notice that i have quite a few collisions incrementing on the interfaces and I believe my configuration is more than likely to blame.  I have done as much troubleshooting as possible but I am not finding what is limiting the throughput.  My CPU is bored almost 100% of the time, even with heavy traffic traversing the router.  My memory is also bored.  I thought a fresh set of eyes on the problem may shed some light...

Since the CPU is remaining low I do not believe the router is forced to process these packets in software.

I have attached two images of my 24 hour usage (5 minute increments) of both CPU and WAN facing interface...

My current interface config is:

edge3845a#show run int gi0/0

Building configuration...

Current configuration : 363 bytes


interface GigabitEthernet0/0

ip address dhcp

no ip proxy-arp

ip flow ingress

ip nat outside

ip virtual-reassembly in drop-fragments

logging event subif-link-status

load-interval 30

duplex auto

speed auto

media-type rj45

no cdp enable


See below output showing collisions:

edge3845a#show int gi0/0

GigabitEthernet0/0 is up, line protocol is up

  Hardware is BCM1125 Internal MAC, address is 0024.c4b9.e1b0 (bia 0024.c4b9.e1b0)

  Internet address is

  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full Duplex, 1Gbps, media type is RJ45

  output flow-control is XON, input flow-control is XON

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  30 second input rate 777000 bits/sec, 77 packets/sec

  30 second output rate 46000 bits/sec, 59 packets/sec

     338341298 packets input, 590212818 bytes, 0 no buffer

     Received 4 broadcasts (0 IP multicasts)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 4294899676 multicast, 0 pause input

     181774919 packets output, 3635425020 bytes, 0 underruns

     0 output errors, 3758022391 collisions, 1 interface resets

     0 unknown protocol drops

     0 babbles, 4294705023 late collision, 0 deferred

     2 lost carrier, 0 no carrier, 0 pause output

     0 output buffer failures, 0 output buffers swapped out

edge3845a#show controllers gigabitEthernet 0/0

Interface GigabitEthernet0/0 (idb 0x692D67D0)

Hardware is BCM1125 Internal MAC (Revision A3)

  network link is up 

  Config is Auto Speed, Auto Duplex

  Selected media-type is RJ45

  SFP is not present

MAC Registers:

ds->rx_all_multicast = 0x0

  mac_hash_0_0 =   0x0000000000000000

  mac_hash_1_0 =   0x0000000000000000

  mac_hash_2_0 =   0x0080000400000000

  mac_hash_3_0 =   0x0000000000000000

  mac_hash_4_0 =   0x0000000000000000

  mac_hash_5_0 =   0x0000000000000000

  mac_hash_6_0 =   0x0001000000000000

  mac_hash_7_0 =   0x0000000000000000

  mac_admask_0 =     0x0000FFFFFFFFFFFF, mac_admask_1  = 0x0000000000000000

  mac_cfg =          0x000000C8000A0176, mac_thrsh_cfg = 0x0000080400087804

  mac_vlantag =      0x0000000000000000, mac_frame_cfg = 0x05F4400000280200

  mac_adfilter_cfg = 0x0000000000000F28, mac_enable    = 0x0000000000000C11

  mac_status =       0x0000000000000000, mac_int_mask  = 0x00004F0000C300C3

  mac_txd_ctl =      0x000000000000000F, mac_eth_addr  = 0x0000B0E1B9C42400

  mac_fifo_ptrs =    0x05F4400000280200, mac_eopcnt    = 0x000044000F0F0F0F

  MAC RX is enabled  RX DMA - channel 0 is enabled, channel 1 is disabled

  MAC TX is enabled  TX DMA - channel 0 is enabled, channel 1 is disabled

  Device status = 1000 Mbps, Full-Duplex

PHY registers



  Register 0x00:   1000  796D  0020  60C1  05E1  C5E1  000D  2001

  Register 0x08:   4B75  0200  7800  0000  0000  0000  0000  3000

  Register 0x10:   0000  2F00  0000  0000  0000  xxxx  xxxx  xxxx

  Register 0x18:   shdw  871F  0000  FFFF  shdw  shdw  8000  0000

  Shadow Registers for 0x18

        shadow-addr 0x0000 val 0400

        shadow-addr 0x0001 val 0001

        shadow-addr 0x0002 val 0282

        shadow-addr 0x0004 val 0004

        shadow-addr 0x0007 val 7067

  Shadow Registers for 0x1C

        shadow-addr 0x0002 val 0800

        shadow-addr 0x0003 val 0C00

        shadow-addr 0x0004 val 100C

        shadow-addr 0x0005 val 141F

        shadow-addr 0x0008 val 2144

        shadow-addr 0x0009 val 2408

        shadow-addr 0x000A val 2801

        shadow-addr 0x000D val 3410

        shadow-addr 0x000E val 3863

        shadow-addr 0x000F val 3C00

        shadow-addr 0x0018 val 6004

        shadow-addr 0x001A val 6903

        shadow-addr 0x001B val 6C87

        shadow-addr 0x001C val 7000

        shadow-addr 0x001D val 7400

        shadow-addr 0x001E val 78E2

        shadow-addr 0x001F val 7CA8

  Shadow Registers for 0x1D

        shadow-addr 0x0000 val 054F

        shadow-addr 0x0001 val 8800

Internal Driver Information:

  lc_ip_turbo_fs = 0x0, ip_routecache = 0x11 (dfs = 0/mdfs = 0)

  rx cache size = 768, rx cache end = 512

  max_mtu = 1524

  ring sizes: RX = 256, TX = 256

  rx_particle_size: 1536

Rx Channel 0:

  dma_config0 =     0x0010002001000888, dma_config1 =    0x002A000000600029

  dma_dscr_base =   0x000000000DC20C80, dma_dscr_cnt =   0x0000000000000100

  dma_cur_dscr_a =  0x000030000DC66A92, dma_cur_dscr_b = 0x0100000000000000

  dma_cur_daddr  =  0x000100000DC213E0

  rxring = 0x2DC20C80, shadow = 0x692D8C30, head = 118 (0x2DC213E0)

  rx_overrun=0, rx_nobuffer=0, rx_discard=0

  Error Interrupts: rx_int_dscr = 0, rx_int_derr = 0, rx_int_drop = 0

Tx Channel 0:

  dma_config0 =     0x000000000100108C, dma_config1 =    0x00A9000000000010

  dma_dscr_base =   0x000000000DC21CC0, dma_dscr_cnt =   0x0000000000000000

  dma_cur_dscr_a =  0x800000000E5EE12A, dma_cur_dscr_b = 0x00F0000000004603

  dma_cur_daddr  =  0x000000000DC22A30

  txring = 0x2DC21CC0, shadow = 0x692D9064, head = 215, tail = 215, tx_count = 0

  Error Interrupts: tx_int_dscr = 0, tx_int_derr = 0, tx_int_dzero = 0

  chip_state = 2, ds->tx_limited = 0

  throttled = 0, enabled = 0, disabled = 0

  reset=2(init=1, restart=1), auto_restart=2

  tx_underflow = 0, tx_overflow = 0

  rx_underflow = 0, rx_overflow = 0, filtered_pak=0

  descriptor mismatch = 0, fixed alignment = 0

  bad length = 0 dropped, 0 corrected

  unexpected sop = 0

Software MAC address filter(hash:length/addr/mask/hits):

need_af_check = 0

  0x00:  0  ffff.ffff.ffff  0000.0000.0000         0

  0x74:  0  0024.c4b9.e1b0  0000.0000.0000 338362995

  0xC0:  0  0180.c200.0002  0000.0000.0000         0

  0xC0:  1  0100.0ccc.cccc  0000.0000.0000         0

  0xC5:  0  0180.c200.0007  0000.0000.0000         0

Address Filter:

  Promiscuous mode OFF

  Multicast software filter needed: 1

  Exact match table (for unicast, maximum 8 entries):

    Entry 0 MAC Addr = 0024.c4b9.e1b0

    (All other entries are empty)

  Hash match table (for multicast, maximum 8 entries):

    Entry 0 MAC Addr = 0180.c200.0007

    Entry 1 MAC Addr = 0180.c200.0002

    Entry 2 MAC Addr = 0100.0ccc.cccc

    (All other entries are empty)


  Rx Bytes                444355328899   Tx Bytes                 98888958847

  Rx Good Packets            338362998   Tx Good Packets            181788025

  Rx Multicast                       0

  Rx Broadcast                       2

  Rx Bad Pkt Errors                  0   Tx Bad Pkt Errors                  0

  Rx FCS Errors                      0   Tx FCS Errors                      0

  Rx Runt Errors                     0   Tx Runt Errors                     0

  Rx Oversize Errors                 0   Tx Oversize Errors                 0

  Rx Length Errors                   0   Tx Collisions                      0

  Rx Code Errors                     0   Tx Late Collisions                 0

  Rx Dribble Errors                  0   Tx Excessive Collisions            0

                                         Tx Abort Errors                    0

If you have any thoughts about what the problem may be I would appreciate the feedback.  I am really trying to build on my troubleshooting skills and this is a great opportunity to learn.

Thank you to everyone in advance!

smitesh kharecha

Hi Jeffrey,

Collision are sign of duplex mismatch...

Try hard coding your interface to 100 /  Full...



PS: Please rate helpful posts.

Change was made, let's see if it does any good.  I beleive I may have had this hard coded during my troubleshooting process... but I will try it again to confirm.

edge3845a#show run int gi0/0

Building configuration...

Current configuration : 363 bytes


interface GigabitEthernet0/0

ip address dhcp

no ip proxy-arp

ip flow ingress

ip nat outside

ip virtual-reassembly in drop-fragments

logging event subif-link-status

load-interval 30

duplex full

speed 1000

media-type rj45

no cdp enable


This appears to have eliminated incrementing collisions, but the speeds are still exactly where they were.  Any ideas to increase the throughput?


I'm doubting the device opposite your cisco, in terms of speed and Duplex.

Can you just  once more confirm speed and duplex on both the devices and preferrable hard code them.



Jeffrey Simon

When I set everything to auto it does auto-negotiate to 1000/full as it should. It also makes sense that the ISP's device is configured correctly since I am getting correct speeds with their router.

Sent from Cisco Technical Support iPhone App

Collisions have stopped incrementing completely but it seems to have nothing to do with my bandwidth problem.  Anyone have thoughts as to what could be the culprit?