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Updated Data Model Limitations (markdown)

Jeremy Stretch 2022-08-18 10:48:18 -04:00
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Data-Model-Limitations.md

@ -2,47 +2,11 @@ NetBox is an extremely powerful tool for modeling network components and topolog
**Physical Modeling**
* [Breakout Cables](#breakout-cables)
* [Combo Ports](#combo-ports)
* [Data Center Fabric Switches](#data-center-fabric-switches)
**Logical Modeling**
* [NHRP IP Addressing (VRRP/HSRP/etc.)](#nhrp-ip-addressing)
# Physical Modeling
## Breakout Cables
A breakout cable is a special type of cable which connects a single termination on one side to multiple terminations on the other. A common example is a cable which connects four 10 Gigabit Ethernet interfaces to a single channelized 40 Gigabit Ethernet interface. It looks like this:
[[images/40ge_breakout_cable_dac.jpg]]
Channelized interfaces are tricky to model because they combine four discrete interfaces into a single physical termination point. For example, a channelized 40GE interface on Junos will appear to the device as four individual 10GE interfaces:
```
xe-0/0/0:0
xe-0/0/0:1
xe-0/0/0:2
xe-0/0/0:3
```
Although they share a physical termination point, each of these functions as an individual interface: Each can be enabled or disabled and configured without consideration of its peers, and each one passes data back and forth to exactly one other interface on the other end of the cable. For these reasons, NetBox models each 10GE channel as its own interface.
This poses a problem for the cable model, which expects and supports only a single interface assignment to either of its two ends.
### Suggested Approach
The recommended approach for modeling breakout cables is to create a separate cable instance for each channelized interface. Although not technically correct, it is perhaps the "least incorrect" possible deviation and ensures that all functions and configurations beyond the physical termination details can be reliably modeled.
```
Device A [xe-0/0/0:0] ---(Cable 1)--- [eth0] Device B
Device A [xe-0/0/0:1] ---(Cable 2)--- [eth0] Device C
Device A [xe-0/0/0:2] ---(Cable 3)--- [eth0] Device D
Device A [xe-0/0/0:3] ---(Cable 4)--- [eth0] Device E
```
## Combo Ports
It's very common for certain lower-end branch or SMB network devices to make a logical interface available via one of two physical connections (typically twisted pair copper or SFP). For example, the Juniper ACX1100-AC provides a set of four copper and four SFP interfaces numbered 0/1/0 through 0/1/3: Each position can utilize either the copper port _or_ its SFP peer, but not both.