While answering these questions, please refer to the material at this link:

https://techzone.cisco.com/t5/XR-Platform-Independent-Topics/IOS-XR-MTU/ta-p/225756

1. Second paragraph under Overview section, consisting of this sentence:So there is an MTU per interface, layer, protocol.

First - we need either an 'and', or an 'or' before the last word in the list - 'protocol'. Which is it?

[Your answer]: and

Next, at a logical level, the MTU is for a communications protocol of a layer - and the layer is allowed to transmit over an interface.

So, is it correct to say the MTU is for each interface, layer, and/or protocol ? Isn't the MTU a measurement associated with only a protocol? Would it be technically correct to insert an ‘and’ or an ‘or’ – or should we be rewriting that sentence?

[Your answer]: I think “and” is fine.

2. Third paragraph under Overview section, the lead-in sentence that introduces the bullet list:

These are the concepts for the MTU in IOS XR:

What follows are two bullets in a list that do not read as general 'concepts'. They read as characteristics of MTU as implemented in Cisco IOS XR. Is that correct?

If yes, may we replace the word 'concepts' with ‘characteristics’?

[Your answer]: yes

3. Last sentence in second bullet point (in Overview section):You first need to increase the interface "mtu" command to make sure that the layer 2 interface payload is large enough to carry a 1508 bytes MPLS frame.

A command cannot be increased – isn’t it? It is not clear what the user needs to increase first. Is it just the MTU?

Please provide a re-written sentence:

[Your answer]:

To transmit a 1508 byte MPLS frame on an Ethernet interface, the interface MTU must be increased to 1522, or an higher value, to ensure that the layer 2 interface payload is large enough to carry the MPLS frame.

4. Consistency of terms.We need to be consistent in the use of MTU and "mtu". (In the material they are used interchangeably.)

Is this correct:

MTU is used when we refer to the maximum transmission unit.

"mtu" is used when we refer to the command, and must always be depicted thus: 'the "mtu" command'.

[Your answer]:

It appears the author uses quotes to indicate configuration commands “mtu”, ipv4 mtu”, “mpls mtu” .I’m not sure this is in accordance with CDC quidelines and if not should be changed.

The author sometimes uses MTU and sometimes mtu in general discussion. I don’t have a preference if you make them all upper or lower case. I think in general discussion it reads better in lower case.

5. Structure of the materialThere is a mix-up in the sections that follow, and most sections do not have a lead-in sentence to introduce the bullet points they contain.

I am explaining what the gap is for each section in six parts (5.a. to 5g.); please arrange to provide the missing information.

5. a.

The initial Overview section concludes with this last statement:

"We will illustrate these concepts for different types of interfaces."

Ideally, at this point we should list the interfaces, for which the concepts (or characteristics, depending on your answer to Point 2, above) are to be illustrated in the sections that follow.

What are all the different types of interfaces that we are about to detail in the sections that follow this Overview section?

[Your answer]:

Routed L3 interfaces

Routed L3 Subinterfaces

L2VPN L2 interfaces

[In your answer, please provide a list of the different types of interfaces about which the sections that follow provide details. This means that if there are three interfaces listed here (the first one being Routed Interfaces), we must have three corresponding sections that follow. ]

5. b.

The next section is the Routed Interface section. This is one of the “different types of interfaces” – about which we are about to illustrate the MTU concepts.

There is no clue as to what the other interfaces are.

[Your answer]: L2VPN L2 Interfaces is the other type.

"Routed Subinterface" seems to be another type; but as heading levels go, it is under the first Routed Interface section – as a sub-section.

[Your answer]: OK move it under it’s own section.

The Routed Interface section has these sub-headings under it:

Default MTU

Non Default

IOS vs IOS XR

Routed Subinterface

[Your answer]: Move the IOS vs IOS XR to it’s own section I would put this section right after the overview. In the summary state that IOS and IOS-XR behavior will be compared and examples provided for Routed L3 Interfaces, Routed L3 Subinterfaces, and L2VPN L2 interfaces.

The first two sub-headings (Default MTU and Non-Default) have a lead-in sentence that clearly states that these are for Routed Interfaces.

[Your answer]: I think these two subsections Default MTU and Non Default under routed L3 interfaces is fine.

The third sub-heading (IOS vs IOS XR) has no lead-in sentence for the bullet list it contains. (This needs to be corrected). But, first: what is this sub-heading – IOS vs IOS XR - and how is it connected to the Routed

Interfaces section? We need to bring that out in a lead-in sentence in that sub-section - before introducing the bullet that that is there.

[Your answer]: Move the IOS and IOS-XR Comparison to it’s own section after the overview.

[Your answer in 3 parts] In your answer:

Please provide a list of the actual sub-sections under the Routed Interfaces section.

[Your answer]:

Please also explain where the sub-section IOS vs IOS XR fits in. Please provide the lead-in sentence for this section / sub-section. Or, is this sub-heading independent, and not connected? If not connected, what is its connection to the "different types of interfaces" that was stated at the end of the Overview section.

[Your answer]: See above.

Please state whether Routed Subinterface is a sub-section under Routed Interface, or is it a section on its own at level with the Routed Interface section - and one of the "different types of interfaces" that was stated at the end of the Overview section?

[Your answer]: You can move to it’s own section

5. c.

Routed Sub-interface section

This section too does not have a lead-in sentence that is required to introduce the bullet list within this section.

We need a clear lead-in sentence that states what is it that we about to say in this section - and thus introduce the bullet list. Please provide that sentence.

[Your answer]:

The following characteristics apply to routed L3 subinterfaces:

5. d.

The other sections are:

L2VPN

Non EVC (XR12000 and CRS)

EVC (ASR9000)

Are these connected to the "different types of interfaces" that was stated at the end of the Overview section?

[Your answer]: Yes, L2VPN L2 Interfaces

5. e.

The L2VPN has an introductory statement. However, there are no such introductory statements for the other two sections:

Non EVC (XR12000 and CRS)

This section does not have a lead-in sentence to introduce the bullet list that it presents. Please provide a lead-in sentence.

[Your answer]:

Routers like the XR12000 and the Carrier Routing System (CRS) use the traditional configuration for the vlan matching on subinterfaces. The following characteristics apply to L2VPN L2 interfaces on CRS and XR12000 routers that don’t follow the EVC model.

5. f.

EVC (ASR9000)

This section has this statement in the beginning:

On the EVC platforms, we have the ability to do flexible VLAN matching.

So, EVC is a platform. By inference, Non EVC (XR12000 and CRS) are platforms.

We need to have stated somewhere as an introduction - before providing details of these platforms - that sections that follow will detail information about these platforms, in relation to MTU.

A statement similar to this one at the Overview section: "We will illustrate these concepts for different types of interfaces."

What statement – in relationship to MTU – should we state before listing these platform details? And where should we fit in that statement?

[Your answer]:

ASR 9000 use the Ethernet Virtual Circuit (EVC) infrastructure model which allows flexible VLAN matching on L2VPN L2 interfeces and subinterfaces.

The EVC L2VPN L2 interfaces have the following characteristics:

5. g. My recommendation

In order to arrive at the answers to the questions about the structure of this material (Questions 5.a. to 5.f.), please complete this visual representation of the structure, fitting in all the headings and sub-headings in the way the material must be structured:

Overview

Routed Interfaces

Default MTU

Non Default

Next Level 1 Heading

Its 1st sub-heading

Its 2nd sub-heading

Please arrange these five headings or sub-headings within the above structure:

IOS vs IOS XR, Routed Subinterface , L2VPN, Non EVC (XR12000 and CRS), EVC (ASR9000),

[Your answer]:

Overview

Comparison of IOS and IOS XR

Routed L3 Interfaces

Characteristics

Default MTU

Non Default

Routed L3 Sub-interfaces

Characteristics

Example

L2VPN L2 Interface

Characteristics

Example

EVC (ASR9000

Non EVC (XR12000 and CRS)