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SkellBasher
Yes Sorto, I'll take my Prozac
join:2000-10-22
North Tonawanda, NY
| reply to Champer
Re: Remaining Florida Markets
said by Champer  :He never said CMTS server, he said CMTS devices, which, if you look at your networking dictionary, would be considered appropriate. Personal foul, half the distance to the goal. Well, technically he said "Motorola UBR server", which by definition doesn't exist since UBR in and of itself is a Cisco designation, so after checking with the War Room in Toronto, the play stands as called.
Yeah Hob, how do I remember those days... I've never gotten around to looking it up, but I still think those things were configurable so that was not required. If you come across one destined for the scrap heap, let me know. Wouldn't mind one for my lab.  | |
dadarkside
Premium
join:2006-05-20
The Moon
| The Cisco 7246 under certain older code was susceptible to MAC forwarding table corruption. To prevent that, you configure the UBR to maintain a fixed table (ARP aging). Tis saved memory for other processes, but it caused issues when the CPE changes.
The UBR 10K, which is a much more "robust" chassis, and was used widely in parts of Florida, Ohio and Virginia never had this issue, as the chassis had a much beefier CPU, more memory and cleaner running code.
As for the Cisco UBR being a dog...well, the older 7246 chassis was limited, but generally stable, as long as you didn't push it too hard. The UBR 10K, however, is probably one of the BEST CMTS Chassis' I have ever worked with. I have seen them support 20,000 customers without issue. | |
hobgoblin
Sortof Agoblin
Premium
join:2001-11-25
Orchard Park, NY
clubs:
| said by dadarkside :The Cisco 7246 under certain older code was susceptible to MAC forwarding table corruption. To prevent that, you configure the UBR to maintain a fixed table (ARP aging). Tis saved memory for other processes, but it caused issues when the CPE changes. The UBR 10K, which is a much more "robust" chassis, and was used widely in parts of Florida, Ohio and Virginia never had this issue, as the chassis had a much beefier CPU, more memory and cleaner running code. As for the Cisco UBR being a dog...well, the older 7246 chassis was limited, but generally stable, as long as you didn't push it too hard. The UBR 10K, however, is probably one of the BEST CMTS Chassis' I have ever worked with. I have seen them support 20,000 customers without issue. Thanks for clearing this up!
Hob
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"A foolish consistency is the hobgoblin of little minds."
- Ralph Waldo Emerson
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SkellBasher
Yes Sorto, I'll take my Prozac
join:2000-10-22
North Tonawanda, NY
| reply to dadarkside
Bravo!! Thanks for satisfying my curiosity!!
Those 10K's do look pretty darn sweet, wouldn't mind fiddling with one someday, although that's not going to happen where I'm at now.
As least I hope not, I have enough to worry about now!! :-p | |
swintec
Premium
join:2003-12-19
Alfred, ME
 ·RapidVPS
·surpasshosting
 ·Sprint Mobile Broa..
 ·VoicePulse
 ·RoadRunner Cable
| reply to dadarkside
said by dadarkside :The Cisco 7246 under certain older code was susceptible to MAC forwarding table corruption. To prevent that, you configure the UBR to maintain a fixed table (ARP aging). Tis saved memory for other processes, but it caused issues when the CPE changes. The UBR 10K, which is a much more "robust" chassis, and was used widely in parts of Florida, Ohio and Virginia never had this issue, as the chassis had a much beefier CPU, more memory and cleaner running code. As for the Cisco UBR being a dog...well, the older 7246 chassis was limited, but generally stable, as long as you didn't push it too hard. The UBR 10K, however, is probably one of the BEST CMTS Chassis' I have ever worked with. I have seen them support 20,000 customers without issue. When you say MAC forwarding table in regards to the CMTS/Chassis, do the CMTS's forward/handle traffic with the customer modems via MAC addresses, since, up to that point the network is still fairly localized/closed between the modem and CMTS? | |
dadarkside
Premium
join:2006-05-20
The Moon
| All CMTS Chassis like the Cisco UBR the Motorolla BSR the ADC/BigBand Cuda have routing tables. The IP Address of the CPE (home computer or router), when it comes on line is granted an entry in the forwarding table....meaning this machine with this known good IP address is sending data in and that data needs to be forwarded correctly.
Now, an IP address is actually a logical assignment by some human effort. Machines care less about what IP address they have, machines really work via the MAC hardware address of the NIC Card or Ethernet port.
The MAC forwarding table is the table that ties the IP Address of the CPE to the MAC Hardware address of the NIC card and associates it to the hardware port the CPE is connecting thru.
Your Home Computer also has a forwarding table, and it too is populated by IP addresses that are associated to MAC addresses. The protocol that handles association between "Logical" IP addressing and "Physical" MAC addressing is known as ARP or Address Resolution Protocol.
You can view your home computer forwarding table by opening a command prompt and typing the following command:
arp -a [ENTER]
Every single device that communicates via Ethernet will use the ARP protocol to maintain it's forwarding table. And the behavior of that forwarding table can be manipulated.
You can make STATIC or FIXED MAC address assignments, you can define how long an address is "live" in that table, in some cases you can even limit the size of the table.
On to the Modem....
The Modem, once it's registered, is little more than an "authorized" Docsis protocol bridge between the CMTS and the Home Computer. The home computer doesn't speak in Docsis, it speaks "Ethernet", but the Cable plant was built to conform to Docsis. This requires Docsis speaking devices at either end to do the translation so that the network "seems" like plain old ethernet to the home computer. I refer to the docsis bridging relationship between the CMTS and the Cable Modem.
So, yes, the Modem has an entry in the CMTS' MAC forwarding table, but it also has hardware address entries in Docsis specific tables on the CMTS as well. But aside from DHCP traffic every few days, the ONLY traffic directed at the modem, is Docsis "link" management,(T3, T4, ranging, you've seen these messages in Modem log posts) so the Modem itself, really doesn't communicate much with the CMTS at the IP addressing layer. | |
SkellBasher
Yes Sorto, I'll take my Prozac
join:2000-10-22
North Tonawanda, NY
| reply to swintec
As an extension of what dadarkside has stated, there is another table that is populated with layer 2 addresses. This table holds the layer two address of the cable modem, and another entry for each layer two device behind that modem that's allowed to pass traffic. It serves a couple of purposes.
When a modem is brought online, it get a parameter assigned to it that defines how many layer two device are allowed to pass traffic through it. It's generally set to 1, for a single IP. When end users purchase a multiple IP product, that parameter is changed to match the number of IPs and end user is allowed.
The modem will snag the source MACs out of the first frames it sees when it comes up, and populate an internal table with them. Only traffic from these MACs will ever be bridged out by the modem; everything else is silently dropped. This MAC remains in the table until it hasn't seen traffic from this MAC in a defined time period (depending on make and modem of modem) or the modem is reset. This is why techs always had people restart modems when they changed machines; it's the fastest way to clear this out.
On Cisco UBRs, the same thing happens on the CMTS side of things. However, it's generally not advisable to bounce an entire UBR to clear it out. On some UBRs back in the day (apparently dictated by code rev), these layer two CPE addresses would automatically change on the UBR when the customer bounced their modem and allowed that traffic to pass. On others, (notably the inherited infrastructure from Prestige and I _think_ the Palm Beach stuff swapped from Comcast), this entry had to be allowed to age out or be manually cleared. Usually a manual clear was the way to go, since the end user was on the phone.
I believe I read a document a long time ago that described how the UBR would alsoe use this modem/CPE association to fast switch traffic to the appropriate cable interface, but that was a long time ago, and I may be recalling it wrong. | |
hobgoblin
Sortof Agoblin
Premium
join:2001-11-25
Orchard Park, NY
clubs: | 15 yard penalty and loss of down for being very boring.
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SkellBasher
Yes Sorto, I'll take my Prozac
join:2000-10-22
North Tonawanda, NY
| said by hobgoblin :15 yard penalty and loss of down for being very boring. Sorry, I forgot to take my sarcasm pills today. Or was that anti-sarcasm.....hmmm... | |
TrainBuff
The New Haven Railroad
Premium
join:2003-05-01
Buffalo, NY
clubs:
 ·Verizon FIOS
·RoadRunner Cable
| reply to hobgoblin
said by hobgoblin :15 yard penalty and loss of down for being very boring. After a replay, we find the information informative and there is no penalty.
Sorry Hob!   | |
Champer
join:2004-04-07
Buffalo, NY
clubs:
| reply to SkellBasher
said by SkellBasher :(depending on make and modem of modem) 30 yard penalty for not using grammar check. Exactly what IS a modem of modem anyways? 
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No animals were harmed in the transmission of this post, but the pitbull living next door is living on borrowed time i tell you! | |
SkellBasher
Yes Sorto, I'll take my Prozac
join:2000-10-22
North Tonawanda, NY | Guilty as charged. :-p | |
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