Never ever chain-connect L3 devices. In situation when you need to add additional device to a segment which exists between two routers only you will have to redo wiring and reconnect everything to switch fabric.
![no](http://tiamat.name/wp-content/uploads/2014/12/no.jpg)
All L3 interfaces of all segments should be connected to a switch fabric directly. The only valid reason to connect L3 interfaces back-to-back directly is keeping segments isolated. However, the isolation can be achieved with SVI absence in segment in question.
![yes](http://tiamat.name/wp-content/uploads/2014/12/yes.jpg)
It appeared to be really complicated to find relative information about sizes of transmission units in different levels of TCP/IP stack and completely impossible to find a united chart with their comparison. So, here it is.
Layer |
Protocol |
Header Size |
Recommended size with header included without protocol extensions, ensuring no segmentation on all underlying layers |
Maximum size of transmission unit with protocol extensions |
Transport |
TCP |
20-60B |
1480 Bit |
1 GB |
|
UDP |
8 B |
1480 Bit |
65535 B |
Network |
IPv4 |
20 B – 60 B |
1500 Bit* |
65535 B |
|
IPv6 |
40 B – infinite |
1500 Bit |
4 GB |
Data link |
10/100 Ethernet |
18 B |
1542 bit |
1542 bit |
|
1/10 GB Ethernet |
18 B |
1542 bit |
9000 bit** |
|
10/100 GB Ethernet |
18 B |
1542 bit |
64000 bit*** |
|
802.11 (WIFI) |
34 B |
2312 bit |
2312 bit |
* Fragmentation is widely used in IP protocols
** Jumbo frames are used on high-rate data link protocols, like Gigabit Ethernet or higher
*** is called Super jumbo frame. Not practically used and may not be profitable on a links lower than 10Gbit Ethernet